<PAGE>

   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 1, 2000

                                                      REGISTRATION NO. 333-39492
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                       ----------------------------------

                                AMENDMENT NO. 3
                                       TO
                                    FORM S-3
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933

                       ----------------------------------

                                 SEMITOOL, INC.
             (Exact name of Registrant as specified in its charter)

<TABLE>
<S>                                        <C>                                        <C>
                 MONTANA                                                                             81-0384392
     (State or other jurisdiction of                                                              (I.R.S. Employer
     incorporation or organization)                                                            Identification Number)
</TABLE>

                                 SEMITOOL, INC.
                             655 WEST RESERVE DRIVE
                            KALISPELL, MONTANA 59901
                                 (406) 752-2107
  (Address, including zip code, and telephone number, including area code, of
                   Registrant's principal executive offices)
                       ----------------------------------

                               RAYMON F. THOMPSON
                CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                 SEMITOOL, INC.
                             655 WEST RESERVE DRIVE
                            KALISPELL, MONTANA 59901
                                 (406) 752-2107
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)
                       ----------------------------------

                                   COPIES TO:

                            JUSTIN L. BASTIAN, ESQ.
                             HEIKE E. FISCHER, ESQ.
                            MORRISON & FOERSTER LLP
                               755 PAGE MILL ROAD
                          PALO ALTO, CALIFORNIA 94304
                                 (650) 813-5600

                       ----------------------------------

    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after the effective date of this Registration Statement.

    If the only securities being registered on this form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. / /


    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, as amended (the "Securities Act"), other than securities offered only in
connection with dividend or interest reinvestment plans, check the following
box. /X/


    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. / /
-------------

    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. / /
-------------

    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. / /
                       ----------------------------------


                        CALCULATION OF REGISTRATION FEE



<TABLE>
<CAPTION>
                                                                    PROPOSED MAXIMUM      PROPOSED MAXIMUM
           TITLE OF EACH CLASS OF                AMOUNT TO BE           OFFERING             AGGREGATE             AMOUNT OF
       SECURITIES TO BE REGISTERED(1)            REGISTERED(2)       PRICE PER SHARE    OFFERING PRICE(2)(3)   REGISTRATION FEE
<S>                                           <C>                  <C>                  <C>                   <C>
Common Stock(4).............................
Preferred Stock(5)..........................
Warrants(6).................................      $75,000,000              (2)              $75,000,000           $19,800(10)
Depositary Shares representing Preferred
  Stock(7)..................................
Debt Securities(8)..........................
Warrants to Purchase Debt Securities(9).....
</TABLE>



(1) This Registration Statement also covers contracts which may be issued by the
    Registrants under which the counterparty may be required to purchase Common
    Stock, Preferred Stock, Depositary Shares or Debt Securities.


(2) In no event will the aggregate maximum offering price of all securities
    registered under this Registration Statement exceed $75,000,000. Any
    securities registered hereunder may be sold separately or as units with
    other securities registered hereunder.


(3) The proposed maximum offering price per unit (a) has been omitted pursuant
    to Instruction II.D. of Form S-3 and (b) will be determined, from time to
    time, by the Registrant in connection with the issuance by the Registrant of
    the securities registered hereunder.


(4) Subject to footnote 2, there is being registered hereunder an indeterminate
    number of shares of Common Stock as may be sold, from time to time, by the
    Registrant, including shares of other classes or series of the Registrant's
    capital stock that may be issued upon reclassification of unissued,
    authorized capital stock of the Registrant. There is also being registered
    hereunder an indeterminate number of shares of Common Stock that may be
    issued upon conversion of Preferred Stock or Depositary Shares registered
    hereunder or upon exercise of Warrants registered hereunder, as the case may
    be.


(5) Subject to footnote 2, there is being registered hereunder an indeterminate
    number of shares of Preferred Stock as may be sold, from time to time, by
    the Registrant, or may be issued upon exercise of Warrants registered
    hereunder.


(6) Subject to footnote 2, there is being registered hereunder an indeterminate
    number of Warrants representing rights to purchase Preferred Stock or Common
    Stock registered hereunder.


(7) To be represented by Depositary Receipts representing an interest in all or
    a specified portion of a share of Preferred Stock.


(8) Subject to footnote 2, there is being registered hereunder an indeterminate
    number of Debt Securities as may be sold from time to time by the
    Registrant.


(9) Subject to footnote 2, there is being registered hereunder an indeterminate
    number of warrants representing rights to purchase Debt Securities
    registered hereunder.


(10) Calculated pursuant to Rule 457(o) of the rules and regulations under the
    Securities Act of 1933, as amended. This amount was previously paid with the
    initial filing of this Registration Statement.

                       ----------------------------------

    THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL HEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME EFFECTIVE ON
SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SUCH SECTION 8(A), MAY
DETERMINE.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. A
REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION. THESE SECURITIES MAY NOT BE SOLD NOR MAY
OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION STATEMENT BECOMES
EFFECTIVE. THIS PROSPECTUS SHALL NOT CONSTITUTE AN OFFER TO SELL OR THE
SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE SECURITIES
IN ANY STATE IN WHICH SUCH OFFER, SOLICITATION OR SALE WOULD BE UNLAWFUL PRIOR
TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF ANY SUCH STATE.
<PAGE>

                 SUBJECT TO COMPLETION, DATED SEPTEMBER 1, 2000


PRELIMINARY PROSPECTUS


                                  $75,000,000


                                     [LOGO]


               COMMON STOCK, PREFERRED STOCK, DEPOSITARY SHARES,
                         WARRANTS, DEBT SECURITIES AND
                      WARRANTS TO PURCHASE DEBT SECURITIES


                                ----------------


    We may offer, from time to time, in one or more series or classes and in
amounts, at prices and on terms that we will determine at the time of offering,
with an aggregate public offering price of up to $75,000,000 (or its equivalent
in another currency based on the exchange rate at the time of sale):



    - shares of our common stock;



    - shares of our preferred stock, in one or more series;



    - our depositary shares;



    - our warrants to purchase shares of common stock or preferred stock;



    - our debt securities; and



    - our warrants to purchase debt securities.



    We will provide the specific terms of these securities in supplements to
this prospectus. You should read this prospectus and the applicable supplement
carefully before you invest.



SEE "RISK FACTORS" BEGINNING ON PAGE 3 TO READ ABOUT THE RISKS YOU SHOULD
CONSIDER BEFORE BUYING SHARES OF OUR COMMON STOCK.


THE SECURITIES AND EXCHANGE COMMISSION AND STATE SECURITIES REGULATORS HAVE NOT
APPROVED OR DISAPPROVED THESE SECURITIES, OR DETERMINED IF THIS PROSPECTUS IS
TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.




                 The date of this prospectus is        , 2000.
<PAGE>

                             ABOUT THIS PROSPECTUS



    This prospectus is part of a registration statement that we filed with the
Securities and Exchange Commission using a "shelf" registration process. Under
this shelf process, we may sell any combination of the common stock, preferred
stock, depositary shares, warrants, debt securities and debt warrants described
in this prospectus in one or more offerings up to a total dollar amount of
$75,000,000. This prospectus provides you with a general description of the
securities we may offer. Each time we sell securities, we will provide a
prospectus supplement that will contain specific information about the terms of
that offering. The prospectus supplement may also add, update or change
information contained in this prospectus. You should read both this prospectus
and the applicable prospectus supplement together with additional information
described under the heading "Where You Can Find More Information."



    Unless otherwise indicated or unless the context requires otherwise, all
references in this prospectus to "we," "us," "our" or the "Company" mean
Semitool, Inc. and its subsidiaries. When we refer to our "Charter" we mean our
Restated Articles of Incorporation, as amended.



                      WHERE YOU CAN FIND MORE INFORMATION



    We file annual, quarterly and special reports, proxy statements and other
information with the Securities and Exchange Commission, or the SEC. You may
read and copy any document we file with the SEC at the SEC's public reference
rooms at Room 1024, Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C.
20549, and at the SEC's regional offices at Seven World Trade Center, 13th
Floor, New York, New York 10048, and Citicorp Center, 500 West Madison Street,
Suite 1400, Chicago, Illinois 60661-2511. Please call the SEC at 1-800-SEC-0330
for further information on the public reference rooms. The SEC also maintains a
web site that contains reports, proxy and information statements, and other
information regarding registrants that file electronically with the SEC
(http://www.sec.gov). You can inspect reports and other information we file at
the offices of the National Association of Securities Dealers, Inc., 1735 K.
Street, N.W., Washington, D.C. 20006.



    We have filed a registration statement of which this prospectus is a part
and related exhibits with the SEC under the Securities Act of 1933, as amended,
or the Securities Act. The registration statement contains additional
information about us and the securities. You may inspect the registration
statement and exhibits without charge at the office of the SEC at 450 Fifth
Street, N.W., Washington, D.C. 20549, and you may obtain copies from the SEC at
prescribed rates.



                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE



    The SEC allows us to "incorporate by reference" the information we file with
the SEC, which means that we can disclose important information to you by
referring to those documents. The information incorporated by reference is an
important part of this prospectus. Any statement contained in a document which
is incorporated by reference in this prospectus is automatically updated and
superseded if information contained in this prospectus, or information that we
later file with the SEC, modifies or replaces this information. We incorporate
by reference the following documents we filed with the SEC:



    - our Annual Report on Form 10-K for the year ended September 30, 1999;



    - our Quarterly Reports on Form 10-Q for the quarters ended December 31,
      1999, March 31, 2000 and June 30, 2000;



    - our Proxy Statement on Schedule 14A for our 2000 Annual Meeting of
      Shareholders;



    - our Current Reports on Form 8-K dated July 6, 2000, July 7, 2000 and
      July 10, 2000;



    - our Registration Statement on Form 8-A filed with the Commission on
      September 1, 1988; and


                                       1
<PAGE>

    - each document filed by us pursuant to Sections 13(a), 13(c), 14 and 15(d)
      of the Securities Exchange Act of 1934, as amended, subsequent to the date
      of this Prospectus and prior to the termination of the offering of all
      Securities to which this Prospectus relates.



    You should rely only on the information incorporated by reference or set
forth in this prospectus or the applicable prospectus supplement. We have not
authorized anyone else to provide you with different information. We may only
use this prospectus to sell securities if it is accompanied by a prospectus
supplement. We are only offering these securities in states where the offer is
permitted. You should not assume that the information in this prospectus or the
applicable prospectus supplement is accurate as of any date other than the dates
on the front of these documents.



    Copies of all documents which are incorporated herein by reference (not
including the exhibits to such information, unless such exhibits are
specifically incorporated by reference in such information) will be provided
without charge to each person, including any beneficial owner, to whom this
Prospectus is delivered upon written or oral request. Requests should be
directed to William A. Freeman, Semitool, Inc., 655 West Reserve Drive,
Kalispell, Montana 59901, (406) 752-2107.


                                       2
<PAGE>

                                  RISK FACTORS


    ANY INVESTMENT IN OUR COMMON STOCK INVOLVES A HIGH DEGREE OF RISK. YOU
SHOULD CONSIDER CAREFULLY THE FOLLOWING INFORMATION ABOUT THESE RISKS, TOGETHER
WITH THE OTHER INFORMATION CONTAINED IN THIS PROSPECTUS, BEFORE YOU DECIDE TO
BUY OUR COMMON STOCK. IF ANY OF THE FOLLOWING RISKS ACTUALLY OCCUR, OUR
BUSINESS, FINANCIAL CONDITION, RESULTS OF OPERATIONS AND CASH FLOWS WOULD LIKELY
SUFFER. IN THESE CIRCUMSTANCES, THE MARKET PRICE OF OUR COMMON STOCK COULD
DECLINE, AND YOU MAY LOSE ALL OR PART OF YOUR INVESTMENT.

CYCLICALITY IN THE SEMICONDUCTOR INDUSTRY HAS HISTORICALLY LED TO SUBSTANTIAL
DECREASES IN DEMAND FOR OUR SYSTEMS AND MAY FROM TIME TO TIME CONTINUE TO DO SO.

    Our operating results are subject to significant variation due to the
cyclical nature of the semiconductor industry. Our business depends upon the
capital expenditures of semiconductor manufacturers, which, in turn, depend upon
the current and anticipated market demand for semiconductors and products using
semiconductors. The semiconductor industry experienced a downturn in 1998 and
1999 which seriously harmed our operating results during that period. Typically,
the semiconductor equipment industry has experienced more pronounced decreases
in net sales than the semiconductor industry as a whole. Our net sales decreased
from $194.0 million in fiscal 1997 to $180.5 million in fiscal 1998, and to
$122.5 million in fiscal 1999. Any further downturns in the semiconductor
industry will likely lead to proportionately greater downturns in our net sales.

    Although there are indications that the semiconductor industry may be
improving:

    - the semiconductor industry may experience other, possibly more severe and
      prolonged, downturns in the future;

    - any continued recovery of the semiconductor industry may not result in an
      increased demand by semiconductor manufacturers for capital equipment or
      our products; and

    - the semiconductor industry may not continue to improve.

    Any future downturn in the semiconductor industry, or any failure of that
industry to fully recover from its recent downturn, will harm our business,
financial condition, results of operations and cash flows.

OUR OPERATING RESULTS HAVE IN THE PAST VARIED AND PROBABLY WILL CONTINUE TO VARY
SIGNIFICANTLY IN THE FUTURE FROM QUARTER TO QUARTER, CAUSING VOLATILITY IN OUR
STOCK PRICE.

    Our quarterly operating results have varied significantly in the past and
may continue to do so in the future, which could cause our stock price to
decline. Some of the factors that may influence our operating results and
subject our common stock to extreme price and volume fluctuations include:

    - changes in customer demand for our systems, which is influenced by
      economic conditions in the semiconductor industry;

    - demand for products that use semiconductors;

    - market acceptance of our systems and those of our customers and changes in
      our product offerings;

    - the timing, cancellation or delay of customer orders and shipments;

    - product development costs, including research, development, engineering
      and marketing expenses associated with our introduction of new products
      and product enhancements; and

    - the levels of our fixed expenses relative to our net sales.

                                       3
<PAGE>
    In light of these factors and the cyclical nature of the semiconductor
industry, we expect to continue to experience significant fluctuations in
quarterly and annual operating results. Moreover, many of our expenses are fixed
in the short-term which, together with the need for continued investment in
research and development, marketing and customer support, limits our ability to
reduce expenses quickly. As a result, declines in net sales could harm our
business, financial condition, results of operations and cash flows.

OUR NET SALES MAY VARY SIGNIFICANTLY FROM QUARTER TO QUARTER DUE TO RELATIVELY
SMALL FLUCTUATIONS IN OUR UNIT SALES.

    During any quarter, a significant portion of our net sales may be derived
from the sale of a relatively small number of systems. For example, our batch
processing tools range in price from approximately $15,000 to $3.2 million per
tool and our single wafer processing tools for cleaning, stripping and etching
range in price from $300,000 to $2.2 million per tool. Accordingly, a small
change in the number of tools we sell may also cause significant changes in our
operating results. This, in turn, could cause fluctuations in the market price
of our common stock.

VARIATIONS IN THE AMOUNT OF TIME IT TAKES FOR US TO SELL OUR SYSTEMS MAY CAUSE
FLUCTUATIONS IN OUR OPERATING RESULTS, WHICH COULD CAUSE OUR STOCK PRICE TO
DECLINE.

    Variations in the length of our sales cycles could cause our net sales, and
thus our business, financial condition, operating results and cash flows, to
fluctuate widely from period to period. This variation could cause our stock
price to decline. Our customers generally take a long time to evaluate many of
our products before committing to make a purchase. We expend significant
resources educating and providing information to our prospective customers
regarding the uses and benefits of our systems. The length of time it takes us
to make a sale depends upon many factors, including:

    - the efforts of our sales force and our independent sales representatives;

    - the complexity of the customer's fabrication processes;

    - the internal technical capabilities and sophistication of the customer;
      and

    - capital expenditure budget cycle of our customers.

    Because of the number of factors influencing the sales cycle, the period
between our initial contact with a potential customer and the time when we
recognize revenue from that customer, if ever, varies widely in length. Our
sales cycle typically ranges from one to twelve months. Sometimes our sales
cycle can be much longer, particularly with our international customers. The
subsequent build cycle, or the time it takes us to build a product to customer
specifications after receiving an order, typically ranges from one to six
months. During these cycles, we commit substantial resources to our sales
efforts in advance of receiving any revenue, and we may never receive any
revenue from a customer despite our sales efforts.

    When a customer purchases one of our systems, that customer often evaluates
the performance of the system for a lengthy period before potentially purchasing
any more of our systems. The number of additional products a customer may
purchase from us, if any, oftentimes depends on many factors, including a
customer's capacity requirements. The period between a customer's initial
purchase and subsequent purchases, if any, often varies from two to twelve
months or longer, and variations in length of this period could cause further
fluctuations in our operating results and possibly in our stock price.

                                       4
<PAGE>
RAPID TECHNOLOGICAL CHANGE COULD MAKE OUR PRODUCTS OBSOLETE OR UNMARKETABLE FOR
SPECIFIC APPLICATIONS.

    We operate in an industry that is subject to evolving industry standards,
rapid technological changes, rapid changes in customer demands and the rapid
introduction of new, higher performance systems with shorter product life
cycles. As a result, we expect to continue to make significant investments in
research and development. Although, historically, we have had adequate funds
from operations to devote to research and development, there can be no assurance
that such funds will be available in the future or, if available, that they will
be adequate. Also, we must manage product transitions successfully, since
announcements or introductions of new products by us or our competitors could
adversely affect sales of our existing products because these existing products
can become obsolete or unmarketable for specific purposes. There can be no
assurance that we will be able to develop and introduce new products or
enhancements to our existing products on a timely basis or in a manner which
satisfies customer needs or achieves widespread market acceptance. Any
significant delay in releasing new systems could adversely affect our
reputation, give a competitor a first-to-market advantage or allow a competitor
to achieve greater market share. The failure to adjust to rapid technological
change could harm our business, financial condition, results of operations and
cash flows.

OUR ELECTROCHEMICAL DEPOSITION PRODUCTS MAY BECOME OBSOLETE OR TECHNOLOGICAL
CHANGES MAY REDUCE OR LIMIT INCREASES IN EQUIPMENT CONSUMPTION, PARTICULARLY FOR
COPPER INTERCONNECTS.

    Our business is to a large extent affected by the adoption of our family of
electrochemical deposition tools, primarily for copper interconnect plating
applications. Accordingly, our business would suffer if these products became
obsolete or if sales of these products decreased. Our success depends on our
ability to keep pace with technological changes and advances in the
semiconductor industry and to adapt and improve our products in response to
evolving customer needs and industry trends. Since its inception the
semiconductor industry has experienced rapid technological change in the design,
manufacture, performance and application of ICs and these changes are expected
to continue in the future. Therefore, one or more developments in the
semiconductor industry may render our products obsolete or less important to the
IC manufacturing process, including:

    - increased competition from new or existing competitors who produce
      electrochemical deposition equipment;

    - the adoption of a new process for fabricating interconnects on ICs; and

    - advances in deposition technology that make it possible to deposit metal
      interconnects, such as copper, without our electrochemical deposition
      process.

FAILURE OF OUR PRODUCTS TO GAIN MARKET ACCEPTANCE WOULD ADVERSELY AFFECT OUR
FINANCIAL CONDITION.

    We believe that our growth prospects depend upon our ability to gain
customer acceptance of our products and technology. Market acceptance of
products depends upon numerous factors, including compatibility with existing
manufacturing processes and products, perceived advantages over competing
products and the level of customer service available to support such products.
Moreover, manufacturers often rely on a limited number of equipment vendors to
meet their manufacturing equipment needs. As a result, market acceptance of our
products may be adversely affected to the extent potential customers utilize a
competitor's manufacturing equipment. There can be no assurance that growth in
sales of new products will continue or that we will be successful in obtaining
broad market acceptance of our systems and technology.

    We expect to spend a significant amount of time and resources to develop new
systems and refine existing systems. In light of the long product development
cycles inherent in our industry, these expenditures will be made well in advance
of the prospect of deriving revenue from the sale of any new

                                       5
<PAGE>
systems. Our ability to commercially introduce and successfully market any new
systems is subject to a wide variety of challenges during this development
cycle, including start-up bugs, design defects and other matters that could
delay introduction of these systems to the marketplace. In addition, since our
customers are not obligated by long-term contracts to purchase our systems, our
anticipated product orders may not materialize, or orders that do materialize
may be cancelled. As a result, if we do not achieve market acceptance of new
products, we may not be able to realize sufficient sales of our systems in order
to recoup research and development expenditures. The failure of any of our new
products to achieve market acceptance would harm our business, financial
condition, results of operation and cash flows.

OUR ABILITY TO REDUCE COSTS IS LIMITED BY OUR ONGOING NEED TO INVEST IN RESEARCH
AND DEVELOPMENT.

    Our industry is characterized by the need for continued investment in
research and development as well as customer service and support. As a result of
our need to maintain our spending levels in these areas, our operating results
could be materially harmed if our net sales fall below expectations. In
addition, because of our emphasis on research and development and technological
innovation, our operating costs may increase further in the future. We expect
our research and development expenses to increase in absolute dollars for the
foreseeable future.

IF THE SEMICONDUCTOR INDUSTRY FAILS TO BROADLY ACCEPT COPPER AS A REPLACEMENT
FOR ALUMINUM AS THE WIRING CHOICE FOR ADVANCED SEMICONDUCTOR DEVICES, OUR COPPER
PLATING PRODUCTS MAY NOT ACHIEVE MARKET ACCEPTANCE.

    Industries that use semiconductors are demanding increasingly complex,
higher performance devices. Traditionally, semiconductor devices have used
aluminum alloys to connect the transistors. However, we believe that as
interconnects become increasingly smaller, copper is evolving as a replacement
for aluminum as the wiring choice for advanced ICs. Our plating products are
designed for plating copper on the wafer for copper interconnects and for
cleaning the wafer after the plating process. If the semiconductor industry as a
whole does not transition to copper interconnects, our copper plating and
associated cleaning products will not achieve market acceptance or
profitability.

INTENSE COMPETITION IN THE MARKETS IN WHICH WE OPERATE MAY REDUCE THE DEMAND FOR
OUR PRODUCTS.

    The markets in which we compete are highly competitive. We face substantial
competition from established competitors, some of which have:

    - greater financial, marketing, technical and other resources;

    - broader product lines;

    - more extensive customer support capabilities; and

    - larger sales organizations and customer bases.

    We may also face competition from new market entrants. Significant
competitive factors in the semiconductor equipment market and other markets, in
which we compete, include system performance and flexibility, cost of ownership,
the size of each manufacturer's installed customer base, customer service and
support capabilities and breadth of product lines. In order to remain
competitive, we must maintain a high level of investment in research and
development, marketing and customer service while controlling operating
expenses. There can be no assurance that we will have sufficient resources to
continue to make such investments or that our products will continue to be
viewed as competitive as a result of technological advances by competitors or
changes in semiconductor processing technology. Our competitors may also
increase their efforts to gain and retain market share through competitive
pricing. Such competitive pressures may necessitate significant price reductions
by us or result in lost orders which could harm our business, financial
condition, results of operations and cash flows.

                                       6
<PAGE>
    Moreover, there has been significant merger and acquisition activity among
our competitors and potential competitors. These combinations may provide such
competitors and potential competitors with a competitive advantage over us by
enabling them to more rapidly expand their product offerings and service
capabilities to meet a broader range of customer needs. Many of our customers
and potential customers are relatively large companies that require global
support and service for their semiconductor manufacturing equipment. Our larger
competitors have more extensive infrastructures than we do, which could place us
at a disadvantage when competing for the business of global semiconductor device
manufacturers.

    We expect our competitors to continue to improve the design and performance
of their products. There can be no assurance that our competitors will not
develop enhancements to, or future generations of, competitive products that
will offer superior price or performance features, or that new processes or
technologies will not emerge that render our products less competitive or
obsolete. As a result of the substantial investment required to integrate
capital equipment into a production line, we believe that once a manufacturer
has selected certain capital equipment from a particular vendor, the
manufacturer generally relies upon that vendor to provide equipment for the
specific production line application and may seek to rely upon that vendor to
meet other capital equipment requirements. Accordingly, we may be at a
competitive disadvantage for a protracted period of time with respect to a
particular customer if that customer utilizes a competitor's manufacturing
equipment. There can be no assurance that we will be able to compete
successfully in the future.

COMPLIANCE WITH ENVIRONMENTAL REGULATIONS MAY BE VERY COSTLY, AND THE FAILURE TO
COMPLY COULD RESULT IN LIABILITIES, FINES AND CESSATION OF OUR BUSINESS.

    We are subject to a variety of governmental regulations related to the
discharge or disposal of toxic, volatile or otherwise hazardous chemicals.
Current or future regulations could require us to purchase expensive equipment
or to incur other substantial expenses to comply with environmental regulations.
Any failure by us to control the use of, or adequately restrict the discharge or
disposal of, hazardous substances could subject us to future liabilities, result
in fines being imposed on us, or result in the suspension of production or
cessation of our manufacturing operations.

DUE TO OUR SIGNIFICANT LEVEL OF INTERNATIONAL SALES, WE ARE SUBJECT TO
OPERATIONAL, FINANCIAL AND POLITICAL RISKS SUCH AS CURRENCY FLUCTUATIONS,
UNEXPECTED CHANGES IN REGULATORY REQUIREMENTS, TARIFFS, POLITICAL AND ECONOMIC
INSTABILITY, ADVERSE TAX CONSEQUENCES, OUTBREAKS OF HOSTILITIES AND DIFFICULTIES
IN MANAGING FOREIGN SALES REPRESENTATIVES AND STAFFING FOREIGN BRANCH
OPERATIONS.


    Our net sales attributable to customers outside the United States as a
percentage of our total net sales were approximately 35.9% in fiscal 1997, 38.3%
in fiscal 1998, 52.8% in fiscal 1999 and 58.5% in the nine month period ended
June 30, 2000. We expect net sales outside the United States to continue to
represent a significant portion of our future net sales. Sales to customers
outside the United States are subject to various risks, including:


    - exposure to currency fluctuations;

    - political and economic instability, particularly in Taiwan and Korea;

    - unexpected changes in regulatory requirements in each of the countries
      outside the United States in which we operate;

    - tariffs and other market barriers in each of the countries outside the
      United States in which we operate;

    - potentially adverse tax consequences in each of the countries outside the
      United States in which we operate;

                                       7
<PAGE>
    - outbreaks of hostilities, particularly in Taiwan and Korea;

    - difficulties in managing foreign sales representatives and distributors in
      each of the countries outside the United States in which we operate; and

    - difficulties in staffing and managing foreign branch operations in each of
      the countries outside the United States in which we operate.

    In addition, because a majority of our international sales are denominated
in U.S. Dollars, our ability to compete overseas could be adversely affected by
a strengthening U.S. Dollar. Moreover, although we endeavor to meet technical
standards established by foreign standards setting organizations, there can be
no assurance that we will be able to comply with changes in foreign standards in
the future. Our inability to design products to comply with foreign standards or
any significant or prolonged decline in our international sales could harm our
business, financial condition, results of operations and cash flows.

IF THE PROTECTION OF OUR PROPRIETARY RIGHTS IS INADEQUATE, OUR BUSINESS COULD BE
HARMED.

    Our success depends in significant part on the technically innovative
features of our products. We currently hold 74 U.S. patents, some with pending
foreign counterparts, have 118 U.S. patent applications pending and intend to
file additional patent applications as we deem appropriate. There can be no
assurance that patents will issue from any of our pending applications or that
existing or future patents will be sufficiently broad to protect our technology.
While we attempt to protect our intellectual property rights through patents,
copyrights and non-disclosure agreements, there can be no assurance that we will
be able to protect our technology, or that competitors will not be able to
develop similar technology independently. In addition, the laws of certain
foreign countries may not protect our intellectual property to the same extent
as the laws of the United States. Moreover, there can be no assurance that our
existing or future patents will not be challenged, invalidated or circumvented,
or that the rights granted thereunder will provide meaningful competitive
advantages to us. In any of such events, our business, financial condition,
results of operations and cash flows could be harmed.

    There has been substantial litigation regarding patent and other
intellectual property rights in semiconductor-related industries. Although we
are not aware of any infringement by our products of any patents or proprietary
rights of others, further commercialization of our products could provoke claims
of infringement from third parties. In the future, litigation may be necessary
to enforce patents issued to us, to protect trade secrets or know-how owned by
us or to defend us against claimed infringement of the rights of others and to
determine the scope and validity of the proprietary rights of others. Any such
litigation could result in substantial cost and diversion of effort by us, which
by itself could have a material adverse effect on our financial condition,
results of operations and cash flows. Further, adverse determinations in such
litigation could result in our loss of proprietary rights, subject us to
significant liabilities and damages to third parties, require us to seek
licenses from third parties or prevent us from manufacturing or selling our
products, any of which could harm our business, financial condition, results of
operations and cash flows.

PROTECTION OF OUR INTELLECTUAL PROPERTY RIGHTS OR THE EFFORTS OF THIRD PARTIES
TO ENFORCE THEIR OWN INTELLECTUAL PROPERTY RIGHTS AGAINST US, HAS IN THE PAST
RESULTED IN, AND MAY IN THE FUTURE RESULT IN, COSTLY AND TIME-CONSUMING
LITIGATION.

    In order to enforce any patents issued to or licensed by us, or to determine
the scope or validity of a third party's patent or other proprietary rights, we
may be required to initiate litigation. Any such litigation, regardless of
outcome, could be expensive and time consuming, and could subject us to
significant liabilities or require us to re-engineer our product or obtain
expensive licenses from third parties.

                                       8
<PAGE>
    For example, in August 1998, we filed suit against Novellus Systems, Inc. in
the United States District Court for the Northern District of California (Case
No. C-98-3089 DLJ), alleging infringement of two of our patents relating to
single substrate processing tools used in electrochemical deposition of copper
onto semiconductor wafers. We sought damages for past infringement, a permanent
injunction prohibiting future infringement, treble damages for willful
infringement, prejudgment interest and attorneys' fees. Novellus answered the
complaint by denying all of the allegations and counter-claiming for declaratory
judgment of invalidity, noninfringement and attorneys' fees. Novellus filed a
motion for summary judgment of noninfringement, which motion was granted on
March 17, 2000, and judgment was subsequently entered on May 12, 2000 dismissing
the case. We filed an appeal to the United States Court of Appeals for the
Federal Circuit on May 15, 2000, seeking review of the ruling on the motion for
summary judgment. We can provide no assurance of the prospect of our success in
such litigation.

OUR EFFORTS TO PROTECT OUR INTELLECTUAL PROPERTY MAY BE LESS EFFECTIVE IN SOME
FOREIGN COUNTRIES WHERE INTELLECTUAL PROPERTY RIGHTS ARE NOT AS WELL PROTECTED
AS IN THE UNITED STATES.

    In fiscal 1999, approximately 52.8% of our net sales was derived from sales
in foreign countries, including certain countries in Asia such as Japan, Korea
and Taiwan. The laws of some foreign countries do not protect our proprietary
rights to as great an extent as do the laws of the United States, and many U.S.
companies have encountered substantial problems in protecting their proprietary
rights against infringement in such countries, some of which are countries in
which we have sold and continue to sell systems. For example, Taiwan is not a
signatory to the Patent Cooperation Treaty, which is designed to specify rules
and methods for defending intellectual property internationally. In Taiwan, the
publication of a patent prior to its filing would invalidate the ability of a
company to obtain a patent. Similarly, in contrast to the United States where
the contents of patents remain confidential during the patent prosecution
process, the contents of a patent are published upon filing which provides
competitors an advanced view of the contents of a patent application prior to
the establishment of patent rights. There is a risk that our means of protecting
our proprietary rights may not be adequate in these countries. Our competitors
in these countries may independently develop similar technology or duplicate our
systems. If we fail to adequately protect our intellectual property in these
countries, it would be easier for our competitors to sell competing products in
those countries.

WE DEPEND ON OUR KEY CUSTOMERS.


    Our ten largest customers accounted for 52.2% of net sales in fiscal 1997,
54.6% in fiscal 1998, 50.9% in fiscal 1999 and 57.8% in the nine months ended
June 30, 2000. We expect this trend to continue. Although the composition of our
largest customers has changed from year to year, the loss of, or a significant
curtailment of purchases by, one or more of our key customers or the delay or
cancellation of a large order could cause our net sales to decline significantly
which would harm our business, financial condition, results of operations and
cash flows. Similarly, delays in payments by key customers could have a
significant impact on our cash flows.


    There is a limited number of mostly large companies operating in the highly
concentrated, capital intensive semiconductor industry. Accordingly, we expect
that we will continue to depend on a small number of large companies for a
significant portion of our net sales. In addition, as large semiconductor
manufacturers seek to establish closer relationships with their suppliers, we
expect that our customer base will become even more concentrated.

OUR DEPENDENCE ON KEY SUPPLIERS COULD DELAY SHIPMENTS AND INCREASE OUR COSTS.

    Some components and subassemblies included in our products are obtained from
a single source or a limited group of suppliers. The loss of, or disruption in,
shipments from these sole or limited source suppliers could in the short-term
adversely affect our business and results of operations. Further,

                                       9
<PAGE>
a significant increase in the price of one or more of these components could
harm our business, financial condition, results of operations and cash flows.

ANTI-TAKEOVER PROVISIONS IN OUR CHARTER DOCUMENTS COULD ADVERSELY AFFECT THE
RIGHTS OF THE HOLDERS OF OUR COMMON STOCK.

    The anti-takeover provisions of Montana law and our Articles of
Incorporation and bylaws may make a change of control of Semitool difficult,
even if a change of control would be beneficial to our shareholders. Our
Articles of Incorporation authorize our Board of Directors to issue preferred
stock in one or more series and to fix the rights, preferences, privileges and
restrictions granted to or imposed upon any unissued shares of preferred stock
and to fix the number of shares constituting any series and the designations of
such series, without further vote or action by the shareholders. Although we
have no present plans to issue any preferred stock, we view the authorized
preferred stock as a financing vehicle. In addition, under Montana law and our
charter documents, our Board of Directors may adopt additional anti-takeover
measures in the future.

    Any anti-takeover provisions, including any issuance of preferred stock,
could have the effect of discouraging a third party from making a tender offer
or otherwise attempting to gain control of us. In addition, these provisions
could limit the price that investors might be willing to pay in the future for
shares of our common stock.

COMPETITIVE CONDITIONS IN OUR INDUSTRY MAY LEAD TO INCREASED PRICE COMPETITION
OR LOSS OF MARKET SHARE FOR OUR PRODUCTS.

    Due to intense competitive conditions in the semiconductor equipment
industry, we have from time to time selectively reduced prices on our systems in
order to protect our market share, and competitive pressures may necessitate
further price reductions. Our competitors are likely to announce the
introduction of new products or lower prices which will affect the prices of our
systems and the level of discounts we grant our customers. To the extent that
any of our semiconductor equipment systems are not distinguished from those of
our competitors by significant technological advantages, we may experience
increased price competition or loss of market share with respect to those
systems.

WE MUST ATTRACT AND RETAIN KEY PERSONNEL INCLUDING A PRESIDENT AND A VICE
PRESIDENT OF SALES, TO HELP DIRECT AND SUPPORT OUR FUTURE GROWTH. COMPETITION
FOR SUCH PERSONNEL IN OUR INDUSTRY IS HIGH.

    Our success depends to a significant degree upon the continued contributions
of our key management, engineering, sales and marketing, customer support,
finance and manufacturing personnel. The loss of any of these key personnel,
particularly our Chairman, President and Chief Executive Officer Raymon F.
Thompson, who would be extremely difficult to replace, could harm our business
and operating results. We do not have key person life insurance on any of our
executives. From time to time, we search for new members of our key management
team and are currently looking for a president and vice president of sales. In
addition, at times in our industry, we have often experienced significant
employee attrition, and we may experience further attrition in the event of a
future downturn. Further, to support future growth, we will need to attract and
retain additional qualified employees. Competition for such personnel in our
industry is intense, and we may not be successful in attracting and retaining
qualified senior executives and other employees.

WE MANUFACTURE SUBSTANTIALLY ALL OF OUR EQUIPMENT AT A SINGLE FACILITY, AND ANY
PROLONGED DISRUPTION IN THE OPERATIONS OF THAT FACILITY COULD HAVE A MATERIAL
ADVERSE EFFECT ON OUR NET SALES.

    We manufacture substantially all of our equipment in our primary
manufacturing facility located in Kalispell, Montana. Our manufacturing
processes are highly complex and require sophisticated and costly equipment and
a specially designed facility. As a result, any prolonged disruption in the

                                       10
<PAGE>
operations of our manufacturing facility, whether due to technical or labor
difficulties, destruction or damage as a result of a fire or any other reason,
could seriously harm our ability to satisfy our customer order deadlines. If we
cannot timely deliver our systems, our net sales could suffer a material adverse
effect.

WE RELY UPON INDEPENDENT SALES REPRESENTATIVES FOR A SIGNIFICANT PORTION OF OUR
SALES, AND A DISRUPTION IN OUR RELATIONSHIPS WITH THESE REPRESENTATIVES COULD
HAVE A NEGATIVE IMPACT ON OUR SALES IN CHINA, JAPAN AND TAIWAN.

    Historically, a substantial portion of our sales have been made through
independent sales representatives and distributors. Currently, we do not use any
distributors. We expect that sales through independent sales representatives
will represent a material portion of our sales for the next several years. In
particular, all our sales in China and Taiwan and some sales in Japan will
continue to be made through independent sales representatives for the next
several years. In some locations, our independent sales representatives also
provide field service to our customers. The activities of these representatives
are generally not within our control. A reduction in the sales or service
efforts or financial viability of any of our independent sales representatives,
or a deterioration or termination of any of our relationships with them, could
harm our net sales, our financial results and our ability to support our
customers.

SINCE A SUBSTANTIAL PORTION OF OUR NET SALES ARE DERIVED FROM SALES IN FOREIGN
COUNTRIES THAT ARE DENOMINATED IN U.S. DOLLARS, WE COULD EXPERIENCE A
SIGNIFICANT DECLINE IN SALES OR EXPERIENCE COLLECTION PROBLEMS IN THE EVENT THE
U.S. DOLLAR BECOMES MORE EXPENSIVE RELATIVE TO LOCAL CURRENCIES.

    A substantial portion of our international sales are denominated in U.S.
Dollars. As a result, if the U.S. Dollar rises in value in relation to foreign
currencies, our systems will become more expensive to customers outside the
United States and less competitive with systems produced by competitors outside
the United States. Such conditions could negatively impact our international
sales. Foreign sales also expose us to collection risk in the event it becomes
more expensive for our foreign customers to convert their local currencies into
U.S. Dollars.

IF WE DELIVER SYSTEMS WITH DEFECTS, OUR CREDIBILITY WILL BE HARMED AND THE SALES
AND MARKET ACCEPTANCE OF OUR SYSTEMS WILL DECREASE.

    Our systems are complex and sometimes have contained errors, defects and
bugs when introduced. If we deliver systems with errors, defects or bugs, our
credibility and the market acceptance and sales of our systems could be harmed.
Further, if our systems contain errors, defects or bugs, we may be required to
expend significant capital and resources to alleviate such problems. Defects
could also lead to product liability as a result of lawsuits against us or
against our customers. We have agreed to indemnify our customers in some
circumstances against liability arising from defects in our systems. Our product
liability policy currently provides only limited coverage per claim. In the
event of a successful product liability claim, we could be obligated to pay
damages which are not covered by product liability insurance or which are
significantly in excess of our product liability insurance limits.

A SMALL GROUP OF MAJOR SHAREHOLDERS WILL CONTINUE TO HAVE A SIGNIFICANT
INFLUENCE OVER OUR BUSINESS AFTER THIS OFFERING AND COULD DELAY, DETER OR
PREVENT A CHANGE OF CONTROL OR OTHER BUSINESS COMBINATION.


    As of March 31, 2000, Raymon F. Thompson, our Chairman, President and Chief
Executive Officer, held approximately 44.7% of our outstanding stock. In
addition, as of March 31, 2000, our officers and directors as a group held
approximately 45.4% of our outstanding stock. These ownership positions could be
reduced, if Mr. Thompson or any of our other officers or directors sell stock in
this offering. The interests of these shareholders may not always coincide with
our interests or those of our other shareholders. By virtue of their stock
ownership and board representation, these shareholders will


                                       11
<PAGE>

continue to have a significant influence over all matters submitted to our Board
of Directors and our shareholders, including the election of our directors, and
will be able to exercise significant control over our business, policies and
affairs. Through their concentration of voting power, these shareholders, acting
individually or together, could cause us to take actions that we would not
consider absent their influence, or could delay, deter or prevent a change of
control of us or other business combination that might otherwise be beneficial
to our other shareholders.


OUR BACKLOG MAY NOT RESULT IN FUTURE NET SALES.

    We schedule the production of our systems based in part upon order backlog.
Due to possible customer changes in delivery schedules and cancellations of
orders, our backlog at any particular date is not necessarily indicative of
actual sales for any succeeding period. In addition, while we evaluate each
customer order on a case by case basis to determine qualification for inclusion
in backlog, there can be no assurance that amounts included in backlog will
ultimately result in future sales. A reduction in backlog during any particular
period, or the failure of our backlog to result in future sales, could harm our
business.

WE HAVE EXPERIENCED A PERIOD OF RAPID GROWTH AND IF WE ARE NOT ABLE TO
SUCCESSFULLY MANAGE THIS AND FUTURE GROWTH, OUR BUSINESS, FINANCIAL CONDITION
AND RESULTS OF OPERATIONS COULD BE SIGNIFICANTLY HARMED.


    We have recently experienced a significant growth in net sales. Our net
sales increased 96.1% from approximately $86.1 million during the nine months,
ended June 30, 1999 to approximately $168.8 million during the nine months ended
June 30, 2000. In addition, our consolidated orders backlog increased 116.3%
from approximately $49.6 million at June 30, 1999 to $107.3 million at June 30,
2000. We cannot assure you we will be able to continue to maintain or increase
the level of net sales in future periods. Further, this growth has placed, and
is expected to continue to place, a significant strain on our management and
operations. If we are unable to effectively manage this growth, our business,
financial condition and results of operations could be significantly harmed.


OUR STOCK PRICE MAY BE VOLATILE AND OUR COMMON STOCK MAY BE THINLY TRADED, WHICH
COULD CAUSE INVESTORS TO LOSE A SUBSTANTIAL PART OF THEIR INVESTMENTS IN OUR
COMMON STOCK.

    The stock market in general, and the stock prices of technology companies in
particular, have recently experienced volatility which has often been unrelated
to the operating performance of any particular company or companies. If market
or industry-based fluctuations continue, our stock price could decline
regardless of our actual operating performance and investors could lose a
substantial part of their investments. The market price of our common stock will
likely fluctuate in response to a number of factors, including the following:

    - variations in our operating results;

    - announcements by us or our competitors of significant contracts or
      acquisitions;

    - our failure to meet the performance estimates of securities analysts;

    - changes in financial estimates of our net sales and operating results by
      securities analysts;

    - stock market price and volume fluctuations attributable to inconsistent
      trading volume levels; and

    - general stock market conditions.

                                       12
<PAGE>
WE COULD BE SUBJECT TO CLASS ACTION LITIGATION DUE TO STOCK PRICE VOLATILITY,
WHICH, IF IT OCCURS, WILL DISTRACT OUR MANAGEMENT AND COULD RESULT IN
SUBSTANTIAL COSTS OR LARGE JUDGMENTS AGAINST US.

    In the past, securities class action litigation has often been brought
against companies following periods of volatility in the market prices of their
securities. We may be the target of similar litigation in the future. Securities
litigation could result in substantial costs and divert our management's
attention and resources, which could cause harm to our business, financial
condition and results of operations.

WE HAVE BROAD DISCRETION IN HOW WE MAY USE THE OFFERING PROCEEDS AND THE MANNER
IN WHICH WE MAY INVEST THESE PROCEEDS MAY NOT YIELD A FAVORABLE, OR ANY, RETURN
FOR US.


    The net proceeds of this offering are not allocated for specific uses other
than working capital and general corporate purposes, unless otherwise indicated
in the applicable prospectus supplement. Thus, our management has broad
discretion over how the net proceeds of this offering will be used and could
spend the net proceeds in a way with which you may not agree. We cannot assure
you that the net proceeds will be invested in a way that yields a favorable, or
any, return for us.


CHANGES TO ACCOUNTING STANDARDS AND RULES COULD ADVERSELY AFFECT THE AMOUNT AND
TIMING OF RECOGNITION OF REVENUE.


    In December 1999, the Securities and Exchange Commission issued Staff
Accounting Bulletin No. 101, or SAB 101, REVENUE RECOGNITION IN FINANCIAL
STATEMENTS. SAB 101 provides guidance on applying generally accepted accounting
principles to revenue recognition issues in financial statements. When we adopt
SAB 101, currently required by the fourth quarter of fiscal 2001, we expect to
recognize revenue when we substantially complete the terms of the applicable
sales arrangement, which generally occurs upon the customers' acceptance of our
product. While we have not fully assessed the impact on us of the adoption of
SAB 101, we believe that it may require a significant amount of our quarterly
net sales to be deferred. Any change in our revenue recognition policy resulting
from the implementation of SAB 101 would be reported as a change in accounting
principle in the quarter in which we implemented SAB 101, with a cumulative
adjustment in that quarter to reflect the effect of the change. As a result,
while SAB 101 would not affect the fundamental aspects of our operations as
measured by our shipments and cash flows, implementation of SAB 101 could have
an adverse effect on our reported results of operations in the quarter that
SAB 101 is implemented.


                                       13
<PAGE>

                                 SEMITOOL, INC.


    Semitool is a worldwide leader in the design, development, manufacture and
support of high performance wet chemical processing equipment for use in the
fabrication of semiconductor devices. Our primary families of tools include
electrochemical deposition systems for the plating of copper interconnects for
integrated circuits and other metals for various applications, and wafer surface
preparation systems for cleaning, stripping and etching processes. This suite of
technologically innovative batch and single wafer processing tools leverages our
core wet chemical expertise and our more than two decades of innovation and
experience building and supporting production-proven semiconductor fabrication
equipment.

    The manufacturing of integrated circuits, called ICs, requires up to 350
complex and repetitive process steps to layer materials and create various
features on a silicon wafer. Deposition is a process in which a film of either
electrically insulating or conductive material, such as copper, is deposited on
the surface of the wafer. The deposition of these film layers is interspersed
with a number of other processes, including cleaning, stripping and etching,
which selectively remove materials and otherwise condition the surface of the
wafer. The IC manufacturing industry is experiencing several trends that are
increasing the demand for wet chemical processing equipment that enables the
fabrication of advanced ICs. These trends include:

    - development of smaller feature geometries;

    - transition to copper as a material for creating the circuitry, or
      interconnect, between the components of an integrated circuit; and

    - migration to larger (300 millimeter diameter) wafers.

    Our objective is to be the leading provider of innovative wet chemical
processing equipment to IC manufacturers. To achieve this goal, we intend to
pursue the following strategies:

    - maintain and expand our technology leadership by continuing to invest in
      research and development that leverages our wet chemical expertise;

    - offer a broad range of differentiated products for use in diverse IC
      manufacturing process applications;

    - leverage our process expertise across a variety of markets and
      applications; and

    - capitalize on our design and manufacturing expertise.

    With more than 20 years dedicated to the semiconductor and related
industries, we have applied our wet chemical expertise in design, engineering,
process and manufacturing to deliver innovations in electrochemical deposition
and cleaning, stripping and etching processes to our global customer base. Our
customers include many of the major semiconductor device manufacturers
worldwide, including Advanced Micro Devices, Conexant Systems, Fujitsu, IBM,
Infineon, Intel, Lucent Technologies, Maxim Integrated Products, Motorola, NEC,
Philips Semiconductor, Samsung, STMicroelectronics, TSMC and UMC.

    Our principal executive offices are located at 655 West Reserve Drive in
Kalispell, Montana 59901, and our telephone number is (406) 752-2107. Our
website address is www.semitool.com. The information in our website does not
constitute a part of this prospectus and is not incorporated into this
prospectus by reference.


    We own the registered trademark "Semitool." This prospectus also includes
other trademarks and tradenames of Semitool and third parties.


                                       14
<PAGE>

                                USE OF PROCEEDS



    Unless otherwise indicated in the applicable prospectus supplement, we
intend to use the net proceeds of any sale of securities pursuant to this
prospectus for general corporate purposes.



                           DESCRIPTION OF SECURITIES



    Our authorized capital stock consists of 75,000,000 shares of common stock,
no par value, and 5,000,000 shares of preferred stock, no par value.



COMMON STOCK



    As of June 30, 2000, there were 28,296,850 shares of common stock
outstanding, held of record by approximately 128 shareholders. The holders of
common stock are entitled to one vote per share on all matters to be voted upon
by the shareholders, except that upon giving the legally required notice,
shareholders may cumulate their votes in the election of directors. Subject to
preferences that may be applicable to any outstanding preferred stock, the
holders of common stock are entitled to receive ratably such dividends, if any,
as may be declared from time to time by the Board of Directors out of funds
legally available therefor. In the event of a liquidation, dissolution or
winding up of the Company, the holders of common stock are entitled to share
ratably in assets remaining after payment of liabilities, subject to prior
distribution rights of preferred stock, if any, then outstanding. The common
stock has no preemptive or conversion rights or other subscription right. There
are no redemption or sinking fund provisions applicable to the common stock. All
outstanding shares of common stock are fully paid and non-assessable, and the
shares of common stock to be issued upon completion of any offering will be
fully paid and non-assessable.



    The common stock is listed on the Nasdaq National Market System under the
symbol "SMTL." The transfer agent and registrar for our common stock is
BankBoston, N.A.



PREFERRED STOCK



    Under our Articles of Incorporation, as amended, our Board of Directors may
direct the issuance of up to 5,000,000 shares of preferred stock in one or more
series and with rights, preferences, privileges and restrictions, including
dividend rights, voting rights, conversion rights, terms of redemption and
liquidation preferences, that may be fixed or designated by our Board of
Directors without any further vote or action by our shareholders.



GENERAL



    Because our Board of Directors has the power to establish the preferences,
powers and rights of each class of preferred stock, it may afford the holders of
any class of preferred stock preferences, powers and rights, voting or
otherwise, senior to the rights of holders of shares of common stock. The
issuance of preferred stock could adversely affect the voting power of holders
of common stock and the likelihood that such holders will receive dividend
payments and payments upon liquidation and could have the effect of delaying,
deferring or preventing a change in control. We have no present plan to issue
any shares of preferred stock.



    Preferred stock, upon issuance against full payment of the purchase price
therefor, will be fully paid and nonassessable. The specific terms of a
particular class of preferred stock will be described in the prospectus
supplement relating to that class, including a prospectus supplement providing
that preferred stock may be issuable upon the exercise of warrants. The
description of preferred stock set forth below and the description of the terms
of a particular class of preferred stock set forth in a prospectus supplement do
not purport to be complete and are qualified in their entirety by reference to
the Certificate of Designation relating to that class.


                                       15
<PAGE>

    The preferences and other terms of the preferred stock of each class will be
fixed by the Certificate of Designation relating to the class. A prospectus
supplement relating to each class of preferred stock will specify the following
terms:



    - The title and stated value of the preferred stock;



    - The number of shares of the preferred stock offered, the liquidation
      preference per share and the offering price of the preferred stock;



    - The dividend rate(s), period(s), and/or payment date(s) or method(s) of
      calculation thereof applicable to the preferred stock;



    - Whether the preferred stock is cumulative or not and, if cumulative, the
      date from which dividends on the preferred stock will accumulate;



    - The provision for a sinking fund, if any, for the preferred stock;



    - The provision for redemption, if applicable, of the preferred stock;



    - Any listing of the preferred stock on any securities exchange;



    - The terms and conditions, if applicable, upon which the preferred stock
      will be converted into common stock, including the conversion price (or
      manner of calculation thereof);



    - A discussion of any material federal income tax considerations applicable
      to the preferred stock;



    - The relative ranking and preferences of the preferred stock as to dividend
      rights and rights upon liquidation, dissolution or winding up of our
      affairs;



    - Any limitations on issuance of any class of preferred stock ranking senior
      to or on a parity with such class or series of preferred stock as to
      dividend rights and rights upon liquidation, dissolution or winding up of
      our affairs;



    - Any other specific terms, preferences, rights, limitations or restrictions
      of the preferred stock; and



    - Any voting rights of the preferred stock.



RANK



    Unless otherwise specified in the applicable prospectus supplement, the
preferred stock will be, with respect to dividends and upon our voluntary or
involuntary liquidation, dissolution or winding up:



    - senior to all classes or series of common stock and to all of our equity
      securities the terms of which provide that the equity securities shall
      rank junior to the preferred stock;



    - junior to all equity securities that we issue which rank senior to the
      preferred stock; and



    - on a parity with all equity securities that we issued other than those
      that are referred to in the bullet points above.



    The term "equity securities" does not include convertible debt securities.



DEPOSITARY SHARES



GENERAL



    We may issue depositary shares, each of which will represent a fractional
interest of a share of a particular class of preferred stock, as specified in
the applicable prospectus supplement. We will deposit with a depositary (the
"preferred stock depositary") shares of a class of preferred stock represented
by depositary shares pursuant to a separate deposit agreement among us, the
preferred stock depositary


                                       16
<PAGE>

and the holders from time to time of the depositary receipts issued by the
preferred stock depositary which will evidence the depositary shares
("depositary receipts"). Subject to the terms of the deposit agreement, each
owner of a depositary receipt will be entitled, in proportion to the fractional
interest of a share of a particular class of preferred stock represented by the
depositary shares evidenced by the depositary receipt, to all the rights and
preferences of the class of the preferred stock represented by the depositary
shares (including dividend, voting, conversion, redemption and liquidation
rights).



    The depositary shares will be evidenced by depositary receipts issued
pursuant to the applicable deposit agreement. Immediately after we issue and
deliver the preferred stock to a preferred stock depositary, we will cause the
preferred stock depositary to issue the depositary receipts on our behalf. You
may obtain copies of the applicable form of deposit agreement and depositary
receipt from us upon request. The statements made in this section relating to
the deposit agreement and the depositary receipt are summaries of certain
anticipated provisions. These summaries are not complete and may be modified by
the applicable prospectus supplement. For more detail you should refer to the
deposit agreement itself, which will be filed as an exhibit to the registration
statement of which this prospectus is a part or incorporated by reference in
this registration statement by a Form 8-K.



DIVIDENDS AND OTHER DISTRIBUTIONS



    The preferred stock depositary will distribute all cash dividends or other
cash distributions received in respect of a class or series of preferred stock
to the record holders of depositary receipts evidencing the related depositary
shares in proportion to the number of depositary receipts owned by such holders,
subject to certain obligations of holders to file proofs, certificates and other
information and to pay certain charges and expenses to the preferred stock
depositary.



    In the event of a distribution other than in cash, the preferred stock
depositary will distribute property that it receives to the record holders of
depositary receipts entitled to the property, subject to certain obligations of
holders to file proofs, certificates and other information and to pay certain
charges and expenses to the preferred stock depositary, unless the preferred
stock depositary determines that it is not feasible to make the distribution, in
which case the preferred stock depositary may, with our approval, sell the
property and distribute the net proceeds from the sale to the holders.



WITHDRAWAL OF STOCK



    Upon surrender of the depositary receipts at the corporate trust office of
the preferred stock depositary, the holders will be entitled to delivery at the
corporate trust office, or upon each such holder's order, of the number of whole
or fractional shares of the class or series of preferred stock and any money or
other property represented by the depositary shares evidenced by such depositary
receipts. Holders of depositary receipts will be entitled to receive whole or
fractional shares of the related class or series of preferred stock on the basis
of the proportion of preferred stock represented by each depositary share as
specified in the applicable prospectus supplement, but holders of such shares of
preferred stock will not thereafter be entitled to receive depositary shares
therefor. If the depositary receipts delivered by the holder evidence a number
of depositary shares in excess of the number of depositary shares representing
the number of shares of preferred stock to be withdrawn, the preferred stock
depositary will deliver to such holder at the same time a new depositary receipt
evidencing the excess number of depositary shares.



REDEMPTION OF DEPOSITARY SHARES



    Whenever we redeem shares of preferred stock held by the preferred stock
depositary, the preferred stock depositary will redeem as of the same redemption
date the number of the depositary shares representing shares of such class or
series of preferred stock so redeemed, provided we shall have paid in full to
the preferred stock depositary the redemption price of the preferred stock to be


                                       17
<PAGE>

redeemed plus an amount equal to any accrued and unpaid dividends on the
preferred stock to the date fixed for redemption. The redemption price per
depositary share will be equal to the corresponding portion of the redemption
price and any other amounts per share payable with respect to such class or
series of preferred stock. If we redeem fewer than all the depositary shares, we
will select the depositary shares that we will redeem pro rata (as nearly as may
be practicable without creating fractional depositary shares), by lot or by any
other equitable method that we determine.



    From and after the date fixed for redemption, all dividends in respect of
the shares of a class or series of preferred stock so called for redemption will
cease to accrue, the depositary shares called for redemption will no longer be
deemed to be outstanding and all rights of the holders of the depositary
receipts evidencing the depositary shares so called for redemption will cease,
except the right to receive any moneys payable upon redemption and any money or
other property to which the holders of the depositary receipts were entitled
upon redemption upon surrender of the depositary receipts to the preferred stock
depositary.



VOTING OF THE PREFERRED STOCK



    Upon receipt of notice of any meeting at which the holders of a class of
preferred stock deposited with the preferred stock depositary are entitled to
vote, the preferred stock depositary will mail the information contained in the
notice of meeting to the record holders of the depositary receipts evidencing
the depositary shares which represent such class of preferred stock. Each record
holder of depositary receipts evidencing depositary shares on the record date
(which will be the same date as the record date for such class of preferred
stock) will be entitled to instruct the preferred stock depositary as to the
exercise of the voting rights pertaining to the amount of preferred stock
represented by the holder's depositary shares. The preferred stock depositary
will vote the amount of such class or series of preferred stock represented by
the depositary shares in accordance with such instructions, and we will agree to
take all reasonable action which the preferred stock depositary may deem
necessary in order to enable the preferred stock depositary to do so. The
preferred stock depositary will abstain from voting the amount of preferred
stock represented by the depositary shares to the extent it does not receive
specific instructions from the holders of depositary receipts evidencing the
depositary shares. The preferred stock depositary will not be responsible for
any failure to carry out any instruction to vote, or for the manner or effect of
any such vote made, as long as any such action or non-action is in good faith
and does not result from the preferred stock depositary's negligence or willful
misconduct.



LIQUIDATION PREFERENCE



    In the event that we voluntarily or involuntarily liquidate, dissolve or
wind up, the holders of each depositary receipt will be entitled to the fraction
of the liquidation preference accorded each share of preferred stock represented
by the depositary share evidenced by the depositary receipt as set forth in the
applicable prospectus supplement.



CONVERSION OF PREFERRED STOCK



    The depositary shares, as such, will not be convertible into common stock or
any other securities or property. Nevertheless, if stated in the applicable
prospectus supplement relating to an offering of depositary shares, holders may
surrender depositary receipts to the applicable preferred stock depositary with
written instructions to the preferred stock depositary to instruct us to cause
conversion of a class or series of preferred stock represented by the depositary
shares evidenced by the depositary receipts into whole shares of common stock,
other shares of a class or series of preferred stock or other shares of stock,
and we have agreed that upon receipt of these instructions and any amounts
payable, we will cause the conversion of the shares of preferred stock utilizing
the same procedures as those provided for delivery of preferred stock to effect
the conversion. If we convert only a portion of


                                       18
<PAGE>

depositary shares evidenced by a depositary receipt, we will issue a depositary
receipt or receipts for any depositary shares that we do not convert. We will
not issue fractional shares of common stock upon conversion, and if conversion
will result in a fractional share, we will pay an amount in cash by equal to the
value of the fractional interest based upon the closing price of our common
stock on the last business day prior to the conversion.



AMENDMENT AND TERMINATION OF A DEPOSIT AGREEMENT



    The form of depositary receipt evidencing depositary shares which represent
the preferred stock and any provision of the deposit agreement may at any time
be amended by agreement between us and the preferred stock depositary. However,
any amendment that materially and adversely alters the rights of the holders of
depositary receipts or that would be materially or adversely inconsistent with
the rights granted to the holders of the related preferred stock will not be
effective unless such amendment has been approved by the existing holders of at
least two-thirds of the applicable depositary shares evidenced by the applicable
depositary receipts then outstanding. No amendment will impair the right,
subject to certain anticipated exceptions in the deposit agreements, of any
holder of depositary receipts to surrender any depositary receipt with
instructions to deliver to the holder the related class of preferred stock and
all money and other property, if any, represented by the depositary receipt,
except in order to comply with law. Every holder of an outstanding depositary
receipt at the time any such amendment becomes effective will be deemed, by
continuing to hold such depositary receipt, to consent and agree to such
amendment and to be bound by the applicable deposit agreement as amended.



CHARGES OF A PREFERRED STOCK DEPOSITARY



    We will pay all transfer and other taxes and governmental charges arising
solely from the existence of the deposit agreement. In addition, we will pay the
fees and expenses of the preferred stock depositary in connection with the
performance of our duties under the deposit agreement. However, holders of
depositary receipts will pay the fees and expenses of the preferred stock
depositary for any duties requested by the holders to be performed which are
outside of those expressly provided for in the deposit agreement.



RESIGNATION AND REMOVAL OF DEPOSITARY



    The preferred stock depositary may resign at any time by delivering to us
notice of its election to do so, and we may at any time remove the preferred
stock depositary, any such resignation or removal to take effect upon the
appointment of a successor preferred stock depositary. A successor preferred
stock depositary must be appointed within 60 days after delivery of the notice
of resignation or removal and must be a bank or trust company with its principal
office in the United States and a combined capital and surplus of at least
$50,000,000.



MISCELLANEOUS



    The preferred stock depositary will forward to holders of depositary
receipts any reports and communications from us which are received by the
preferred stock depositary with respect to the related preferred stock.



    We will not be liable, and the preferred stock depositary will not be
liable, if we are prevented or it is prevented from or delayed in, by law or any
circumstances beyond its or our control, performing the obligations under the
deposit agreement. Our obligations and the obligations of the preferred stock
depositary under the deposit agreement will be limited to performing our duties
in good faith and without negligence (in the case of any action or inaction in
the voting of a class or series of preferred stock represented by the depositary
shares), gross negligence or willful misconduct. We will not be obligated, and
the preferred stock depositary will not be obligated, to prosecute or defend any
legal


                                       19
<PAGE>

proceeding in respect of any depositary receipts, depositary shares or shares of
a class or series of preferred stock represented thereby unless satisfactory
indemnity is furnished. We may rely on, and the preferred stock depositary may
rely on, written advice of counsel or accountants, or information provided by
persons presenting shares of preferred stock represented thereby for deposit,
holders of depositary receipts or other persons that we believe in good faith to
be competent to give such information, and on documents that we believe in good
faith to be genuine and signed by a proper party.



    If a preferred stock depositary receives conflicting claims, requests or
instructions from any holders of depositary receipts, on the one hand, and from
us, on the other hand, the preferred stock depositary will be entitled to act on
such claims, requests or instructions received by us.



WARRANTS



    We currently have no warrants outstanding (other than options issued under
our stock option plans). We may issue warrants for the purchase of common stock
or preferred stock. We may issue warrants independently or together with any
other securities offered pursuant to any prospectus supplement and warrants may
be attached to or separate from such securities. We will issue each series of
warrants under a separate warrant agreement that we will enter into with a
warrant agent specified in the applicable prospectus supplement. The warrant
agent will act solely as our agent in connection with the warrants of such
series and will not assume any obligation or relationship of agency or trust for
or with any provisions of the warrants. We will set forth additional terms of
the warrants and the applicable warrant agreements in the applicable prospectus
supplement.



    The applicable prospectus supplement will describe the terms of the warrants
in respect of which we are delivering this prospectus, including, where
applicable, the following:



    - the title of the warrants;



    - the aggregate number of the warrants;



    - the price or prices at which the warrants will be issued;



    - the designation, terms and number of shares of preferred stock or common
      stock purchasable upon exercise of the warrants;



    - the designation and terms of any securities with which the warrants are
      issued and the number of any warrants issued with each such security;



    - the date, if any, on and after which the warrants and the related
      preferred stock or common stock will be separately transferable;



    - the price at which each share of preferred stock or common stock
      purchasable upon exercise of the warrants may be purchased;



    - the date on which the right to exercise the warrants will commence and the
      date on which the right will expire;



    - the minimum or maximum amount of the warrants which may be exercised at
      any one time;



    - information with respect to book-entry procedures, if any;



    - a discussion of certain federal income tax considerations; and



    - any other terms of the warrants, including terms, procedures and
      limitations relating to the exchange and exercise of the warrants.


                                       20
<PAGE>

DEBT SECURITIES



GENERAL



    The debt securities may be secured or unsecured and may be senior or
subordinated indebtedness. Unless otherwise specified in the applicable
prospectus supplement, the debt securities are to be issued under an indenture,
as amended or supplemented from time to time, among us and a trustee chosen by
the Company and qualified to act as trustee under the Trust Indenture Act of
1939, as amended. The indenture is subject to, and governed by, the Trust
Indenture Act of 1939, as amended. The statements made in this section relating
to the indenture and the debt securities are summaries of certain provisions of
the debt securities and the indenture. These summaries are not complete. For
more detail you should refer to the indenture, which we have filed as an exhibit
to the registration statement of which this prospectus is a part.



TERM



    We will describe the particular terms of the debt securities offered by a
prospectus supplement in the applicable prospectus supplement, along with any
applicable modifications of or additions to the general terms of the debt
securities as described in this prospectus. Accordingly, for a description of
the terms of any series of debt securities, you must refer to both the
prospectus supplement relating to that series and the description of the debt
securities set forth in this prospectus. A prospectus supplement may change any
of the terms of the debt securities described in this prospectus.



    We may offer under this prospectus up to $75,000,000 (or its equivalent in
another currency based on the exchange rate at the time of sale) aggregate
principal amount of debt securities or if debt securities are issued at a
discount, such principal amount as may be sold for an initial public offering
price of up to $75,000,000. Unless we state otherwise in any prospectus
supplement, we may issue the debt securities in one or more series, as
established from time to time by us. We need not issue all debt securities of
one series at the same time and, unless otherwise provided, a series may be
reopened, without the consent of the holders of the debt securities of that
series, for issuances of additional debt securities of that series.



    We may, but need not, designate more than one trustee under the indenture,
each with respect to one or more series of debt securities. Any trustee may
resign or be removed with respect to one or more series of debt securities, and
a successor trustee may be appointed to act with respect to the series. If two
or more persons are acting as trustee with respect to different series of debt
securities, each such trustee will be a trustee of a trust under the indenture
separate and apart from the trust administered by any other trustee and, except
as we state otherwise in this prospectus, any action to be taken by a trustee
may be taken by each trustee with respect to, and only with respect to, the one
or more series of debt securities for which it is trustee.



    The following summaries set forth certain general terms and provisions of
the indenture and the debt securities. The prospectus supplement relating to the
series of debt securities being offered will contain further terms of the debt
securities, including the following specific terms:



    - the title of the debt securities;



    - the limit on the aggregate principal amount of the debt securities of the
      series that may be authenticated and delivered under the indenture;



    - the date or dates, or the method for determining the date or dates, on
      which we will pay the principal of the debt securities;



    - the rate or rates (which may be fixed or variable), or the method by which
      such rate or rates will be determined, at which the debt securities will
      bear interest, if any;


                                       21
<PAGE>

    - the date or dates (or the method for determining the date or dates) from
      which any interest will accrue, the dates upon which any interest will be
      payable and the record dates for payment of interest (or the method by
      which the record dates will be determined);



    - the place or places, if any, other than or in addition to the Borough of
      Manhattan, The City of New York, where the principal of (and premium, if
      any) and interest, if any, on the debt securities will be payable, where
      the debt securities may be surrendered for conversion or registration of
      transfer or exchange and where notices or demands to or upon us in respect
      of the debt securities and the indenture may be served;



    - any obligation we have to redeem, repay or repurchase the debt securities,
      in whole or in part, at the option of a holder of the debt securities, and
      the period or periods within which, the date or dates on which the price
      or prices at which and the terms and conditions upon which we will redeem,
      repay or repurchase the debt securities;



    - if other than the trustee, the identity of each security registrar and/or
      paying agent;



    - any conversion or exchange provisions of the debt securities;



    - any provisions granting special rights to holders of the debt securities;



    - any deletions from, modifications of, or additions to the events of
      default or covenants by us with respect to the debt securities, whether or
      not such events of default or covenants are consistent with the events of
      default or covenants with the indenture;



    - the person to whom any interest will be payable, if other than the person
      in whose name the debt security is registered; and



    - any other terms of the debt securities and any deletions from or
      modifications or additions to the indenture in respect of the debt
      securities (whether or not consistent with the other provisions of the
      indenture).



    We may issue debt securities at a discount below their principal amount and
provide for less than the entire principal amount of the debt securities to be
payable upon declaration of acceleration of maturity. In such cases, we will
describe any material U.S. federal income tax, accounting and other
considerations in the applicable prospectus supplement.



CONVERSION AND EXCHANGE



    The applicable prospectus supplement will specify the terms and conditions,
if any, on which debt securities of any series are convertible into or
exchangeable for common stock or preferred stock. Such terms may include
provisions for conversion or exchange, either mandatory, at the option of the
holder, or at our option, in which the number of shares of common stock or
preferred stock to be received by the holders of the debt securities would be
calculated according to the market price of common stock or preferred stock as
of a time stated in the prospectus supplement.



DENOMINATIONS AND INTEREST



    Unless we specify otherwise in the applicable prospectus supplement, the
debt securities of any series will be issuable in denominations of $1,000 and
integral multiples thereof. Unless we specify otherwise in the applicable
prospectus supplement, interest on any series of debt securities will be payable
to the person in whose name the security is registered at the close of business
on the record date for such interest at our office. However, unless we provide
otherwise in the applicable prospectus supplement, we may make interest payments
by check mailed to the address of the person entitled to the interest as it
appears in the applicable register for debt securities or by wire transfer of
funds to such person at an account maintained within the United States.


                                       22
<PAGE>

GLOBAL NOTES



    Unless we specify otherwise in the applicable prospectus supplement, the
debt securities of each series will be issued in the form of one or more fully
registered book-entry debt securities of such series (each, a "Global Note")
that will be deposited with, or on behalf of The Depository Trust Company, New
York, New York ("DTC"). Global Notes will be issued in fully registered form.



    We anticipate that the Global Notes will be deposited with, or on behalf of
DTC, and that such Global Note will be registered in the name of Cede & Co.,
DTC's nominee. Unless we specify otherwise in the applicable prospectus
supplement, the Company further anticipates that the following provisions will
apply to the depository arrangements with respect to the Global Notes.



    So long as DTC or its nominee is the registered owner of the Global Notes,
DTC or its nominee, as the case may be, will be considered the sole holder of
the debt securities represented by the Global Note for all purposes under the
indenture. Except as described below, owners of beneficial interests in the
Global Notes will not be entitled to have debt securities represented by such
Global Note registered in their names, will not receive or be entitled to
receive physical delivery of debt securities in certificated form and will not
be considered the owners or holders of the debt securities under the indenture.
The laws of some states require that certain purchasers of securities take
physical delivery of such securities in certificated form; accordingly, such
laws may limit the transferability of beneficial interests in the Global Notes.



    The Global Notes will be exchangeable for certificated debt securities only
if:



    - DTC notifies us that it is unwilling or unable to continue as depository
      or DTC ceases to be a clearing agency registered under the Exchange Act
      (if so required by applicable law or regulation) and, in either case, a
      successor depository is not appointed by us within 90 days after the
      Company receives such notice or becomes aware of such ineligibility;



    - we in our sole discretion determine that the Global Notes shall be
      exchangeable for certificated debt securities; or



    - there shall have occurred and be continuing an event of default with
      respect to debt securities of any series under the indenture and
      beneficial owners representing a majority in aggregate principal amount of
      the debt securities of such series represented by a Global Note advise DTC
      to cease acting as depository. Upon any such exchange, owners of a
      beneficial interest in such Global Note will be entitled to physical
      delivery of individual debt securities of such series in certificated form
      of like tenor, terms and rank, equal in principal amount to such
      beneficial interest, and to have such debt securities in certificated form
      registered in the names of the beneficial owners, which names are expected
      to be provided by DTC's relevant Participants (as identified by DTC) to
      the trustee. Debt securities so issued in certificated form will be issued
      in denominations of $1,000 or any integral multiple thereof, and will be
      issued in registered form only, without coupons.



MERGER, CONSOLIDATION OR SALE OF ASSETS



    Unless we specify otherwise in the applicable prospectus supplement, the
indenture provides that we will not, in any transaction or series of
transactions, consolidate with, or sell, lease, assign, transfer or otherwise
convey all or substantially all of its assets to, or merge with or into any
other person unless:



    - either we are the continuing person or the successor person (if other than
      the Company) formed by or resulting from any such consolidation or merger
      or which shall have received the transfer of such assets shall expressly
      assume payment of the principal of (and premium, if any) and


                                       23
<PAGE>

      interest on all of debt securities, and the due and punctual performance
      and observance of all of the covenants and conditions contained in the
      indenture;



    - immediately after giving effect to the transaction and treating any debt
      which becomes an obligation of ours or any of our subsidiaries as a result
      of such transaction as having been incurred by the Company or such
      subsidiary at the time of such transaction, no event of default under the
      indenture, and no event which, after notice or lapse of time, or both,
      would become an event of default, shall have occurred and be continuing;
      and



    - we deliver to the trustee an officers' certificate and legal opinion
      covering these conditions.



    In the event that we are not the continuing person, then, for purposes of
the second bullet point above, the successor person will be deemed to us.



    Upon any such merger, consolidation, sale, assignment, transfer, lease or
conveyance in which we are not the continuing legal entity, the successor entity
formed by the consolidation or into which we are merged or to which the sale,
assignment, transfer, lease or other conveyance is made shall succeed to, and be
substituted for, and may exercise every right and power of, us under the
indenture with the same effect as if the successor entity has been named as us
in the indenture and we will be released (except in the case of a lease) from
its obligations under the indenture and the debt securities.



EVENTS OF DEFAULT, NOTICE AND WAIVER



    Unless we specify otherwise in the applicable prospectus supplement, the
indenture provides that the following events are "events of default" with
respect to any series of debt securities issued under the indenture:



    - default in the payment of any interest upon any debt security of that
      series when it becomes due and payable, and continuance of that default
      for a period of 30 days;



    - default in the payment of principal of or premium, if any, on any debt
      security of that series when due and payable;



    - default in the performance or breach of any covenant or warranty of the
      Company in the indenture with respect to any debt security of that series
      (other than a covenant or warranty the default or breach of which is
      specifically dealt with in the indenture), which default continues uncured
      for a period of 60 days after receipt of written notice as provided in the
      indenture;



    - default in the payment of an aggregate principal amount exceeding
      $10,000,000 of any evidence of indebtedness of the Company or any
      mortgage, indenture, note, bond, capitalized lease or other instrument
      under which such indebtedness is issued or by which such indebtedness is
      secured, such default having continued after the expiration of any
      applicable grace period and having resulted in the acceleration of the
      maturity of such indebtedness, but only if such indebtedness is not
      discharged or such acceleration is not rescinded or annulled;



    - certain events of bankruptcy, insolvency or reorganization with respect to
      the Company, the Company or any significant subsidiary of the Company (as
      defined in Regulation S-X under the Securities Act); and



    - any other event of default provided with respect to debt securities of
      that series that is described in the applicable prospectus supplement.



    A supplemental indenture establishing the terms of a particular series of
debt securities may delete, modify or add to the events of default described
above.



    No event of default with respect to a particular series of debt securities
necessarily constitutes an event of default with respect to any other series of
debt securities.


                                       24
<PAGE>

    The occurrence of an event of default may constitute an event of default
under our bank credit agreements in existence from time to time. In addition,
the occurrence of certain events of default or an acceleration under the
indenture may constitute an event of default under certain of our other
indebtedness outstanding from time to time.



    If an event of default with respect to debt securities of any series at the
time outstanding occurs and is continuing, then the trustee or the holders of
not less than a majority in principal amount of the outstanding debt securities
of that series may, by a notice in writing to us (and to the trustee if given by
the holders), declare all debt securities of that series to be due and payable
immediately.



    At any time after a declaration of acceleration with respect to debt
securities of any series has been made, but before a judgment or decree for
payment of the money due has been obtained by the trustee, the holders of a
majority in principal amount of the outstanding debt securities of that series
may rescind and annul the acceleration if:



    - we have paid or deposited with the trustee a sum sufficient to pay:



       - all overdue installments of interest on all outstanding debt securities
         of that series;



       - the principal of (and premium, if any, on) any outstanding debt
         securities of that series which have become due otherwise than by such
         declaration of acceleration, and interest thereon at the rates provided
         for in such debt securities; and



    - to the extent lawful, interest upon overdue installments of interest at
      the rate or rates provided in such debt securities; and



    - all events of default with respect to debt securities of that series,
      other than the nonpayment of the principal of (or premium, if any) or
      interest on debt securities of that series which have become due solely by
      such declaration of acceleration, have been cured or waived.



    The indenture also provides that the holders of a majority in principal
amount of the outstanding debt securities of any series may on behalf of the
holders of all debt securities of such series waive any past default under the
indenture with respect to such debt securities and its consequences, except a
default:



    - in the payment of the principal of (or premium, if any) or interest on or
      payable in respect of any debt security of such series; or



    - in respect of a covenant or provision of the indenture which cannot be
      modified or amended without the consent of the holder of each outstanding
      debt security of such series affected.



    If the trustee knows of a default with respect to the debt securities of any
series, the indenture requires the trustee, within 90 days after the default, to
give notice to the holders of such debt securities, unless such default shall
have been cured or waived. However the trustee may withhold notice to the
holders of any debt securities of such series of any default (except a default
in the payment of the principal of (or premium, if any) or interest, if any, on
any debt security of such series) if the trustee determines such withholding is
in the interest of such holders.



    The indenture provides that the trustee will be under no obligation to
exercise any of its rights or powers under the indenture at the request of any
holders of outstanding debt securities, unless the holders offer the trustee
security or indemnity reasonably satisfactory to it against the costs, expenses
and liabilities which might be incurred by it in compliance with such request.
Subject to certain rights of the trustee, the holders of a majority in principal
amount of the outstanding debt securities of any series will have the right to
direct the time, method and place of conducting any proceeding for any remedy
available to the trustee or exercising any trust or power conferred on the
trustee with respect to the debt securities of that series.


                                       25
<PAGE>

    No holder of any debt security of any series will have any right to
institute any proceeding, judicial or otherwise, with respect to the indenture
or for the appointment of a receiver or trustee, or for any remedy under the
indenture, unless:



    - that holder has previously given to the trustee written notice of a
      continuing event of default with respect to debt securities of that
      series; and



    - the holders of a majority in principal amount of the outstanding debt
      securities of that series have made a written request, and offered
      reasonable indemnity, to the trustee to institute the proceeding as
      trustee, and the trustee has not received from the holders of a majority
      in principal amount of the outstanding debt securities of that series a
      direction inconsistent with that request and has failed to institute the
      proceeding within 60 days.



    Notwithstanding the foregoing, the holder of any debt security will have an
absolute and unconditional right to receive payment of the principal of, premium
and any interest on that debt security on or after the due dates expressed in
that debt security and to institute suit for the enforcement of payment.



    The indenture requires us, within 120 days after the end of each fiscal
year, to furnish to the trustee a statement as to compliance with the indenture.
Further, upon any request by us to take any action under the indenture, we will
furnish to the trustee:



    - an officers' certificate stating that all conditions precedent, if any,
      provided for in the indenture relating to the proposed action have been
      complied with; and



    - an opinion of counsel stating that in the opinion of such counsel all such
      conditions precedent, if any, have been complied with.



MODIFICATION AND WAIVER



    We may modify and amend the indenture with the consent of the holders of a
majority in principal amount of the outstanding debt securities of each series
affected by the modifications or amendments except that we may not make any
modification or amendment without the consent of the holders of each affected
debt security then outstanding if that amendment will:



    - change the stated maturity of the principal of (or premium, if any, on) or
      any installment of principal of or interest on such debt security;



    - reduce the principal amount of debt securities or the rate or amount of
      interest on such debt securities, or any premium payable on such debt
      security;



    - adversely affect the right of any holder of debt securities to repayment
      of such debt security at the holder's option;



    - change the place, or the currency, for payment of principal of (or
      premium, if any) such debt security;



    - impair the right to institute suit for enforcement of any payment on or
      with respect to such debt security;



    - reduce the amount of debt securities whose holders must consent to an
      amendment or waiver or reduce the quorum or voting requirements set forth
      in the indenture; or



    - modify any of the foregoing provisions or any of the provisions relating
      to the waiver of certain past defaults or certain covenants, except to
      increase the required percentage to effect such action or to provide that
      certain other provisions may not be modified or waived without the consent
      of the holder of such debt security.


                                       26
<PAGE>

    The holders of a majority in principal amount of the outstanding debt
securities of any series may on behalf of the holders of all debt securities of
that series waive the Company's compliance with certain covenants of the
indenture.



    Modifications and amendments of the indenture may be made by the Company and
the trustee without the consent of any holder of debt securities issued
thereunder for any of the following purposes:



    - to evidence the succession of another person to the Company under the
      indenture;



    - to add to the covenants of the Company for the benefit of the holders of
      the debt securities or to surrender any right or power conferred upon the
      Company in the indenture;



    - to add events of default for the benefit of the holders of all or any
      series of debt securities;



    - to add or change any provisions of the indenture to facilitate the
      issuance of the debt securities in certificated form, provided that such
      action shall not adversely affect the interests of the holders of any debt
      securities in any material respect;



    - to secure the debt securities;



    - to provide for the acceptance of appointment by a successor trustee or to
      facilitate the administration of the trusts under the indenture by more
      than one trustee;



    - to cure any ambiguity, defect or inconsistency in the indenture or to add
      or change any other provisions with respect to matters or questions
      arising under the indenture, provided that such action shall not adversely
      affect the interests of holders of debt securities of any series or any
      related guarantees in any material respect; or



    - to supplement any of the provisions of the indenture to the extent
      necessary to permit or facilitate defeasance and discharge of any series
      of debt securities, provided that such action shall not adversely affect
      the interests of the holders of the debt securities n any material
      respect.



    The indenture provides that in determining whether the holders of the
requisite principal amount of outstanding debt securities of a series have given
any request, demand, authorization, direction, notice, consent or waiver under
the indenture or whether a quorum is present at a meeting of holders of the debt
securities of a series, debt securities of each series owned by the Company or
any other obligor upon such debt securities or any affiliate of the Company or
of such other obligor will be disregarded.



    The indenture contains provisions for convening meetings of the holders of
debt securities of a series. A meeting may be called at any time by the trustee
and also, upon request, by the Company or the Holders of 25% in principal amount
of the outstanding debt securities of such series, in any such case upon notice
given as provided in the indenture. Except for any consent that must be given by
the holder of each debt security affected by certain modifications and
amendments of the indenture, any resolution presented at a meeting or adjourned
meeting duly reconvened at which a quorum is present may be adopted by the
affirmative vote of the holders of a majority in principal amount of the
outstanding debt securities of such series. However, except as referred to
above, any resolution with respect to any request, demand, authorization,
direction, notice, consent, waiver or other action that may be made, given or
taken by the holders of a specified percentage, which is less or more than a
majority, in principal amount of the outstanding debt securities of such series
may be adopted at a meeting or adjourned meeting duly reconvened at which a
quorum is present by the affirmative vote of the holders of such specified
percentage in principal amount of the outstanding debt securities of such
series. Any resolution passed or decision taken at any meeting of holders of
debt securities of any series duly held in accordance with the indenture will be
binding on all holders of debt securities of


                                       27
<PAGE>

such series. The quorum at any meeting called to adopt a resolution, and at any
reconvened meeting, will be persons holding or representing a majority in
principal amount of the outstanding debt securities of any series; provided,
however, that if any action is to be taken at such meeting with respect to a
consent or waiver which may be given by the holders of not less than a specified
percentage, which is less or more than a majority, in principal amount of the
outstanding debt securities of such series, the persons holding or representing
such specified percentage in principal amount of the outstanding debt securities
of such series will constitute a quorum.



    Notwithstanding the provisions described above, the indenture provides that
if any action is to be taken at a meeting of holders of debt securities of any
series with respect to any request, demand, authorization, direction, notice,
consent, waiver or other action that the indenture expressly provides may be
made, given or taken by the holders of a specified percentage in principal
amount of all outstanding debt securities of such series affected thereby:



    - there shall be no minimum quorum requirement for such meeting; and



    - the principal amount of the outstanding debt securities of such series
      that are entitled to vote in favor of such request, demand, authorization,
      direction, notice, consent, waiver or other action shall be taken into
      account in determining whether such request, demand, authorization,
      direction, notice, consent, waiver or other action has been made, given or
      taken under the indenture.



DEFEASANCE OF DEBT SECURITIES AND CERTAIN COVENANTS IN CERTAIN CIRCUMSTANCES



    Legal Defeasance and Covenant Defeasance. Unless we specify otherwise in the
applicable prospectus supplement, the indenture provides that the Company may
elect:



    - to be discharged from any and all obligations in respect of the debt
      securities of any series (except for certain obligations to register the
      transfer or exchange of debt securities of such series, to replace stolen,
      lost or mutilated debt securities of such series, and to maintain paying
      agencies and certain provisions relating to the treatment of funds held by
      paying agents) ("legal defeasance"); or



    - to be released from compliance with the covenants in the indenture
      ("covenant defeasance").



    The Company will be so discharged upon the deposit with the trustee, in
trust, of money and/or Government Obligations that, through the payment of
interest and principal in accordance with their terms, will provide money in an
amount sufficient to pay and discharge each installment of principal (and
premium, if any) and interest on the debt securities of that series on the
scheduled due dates or the applicable redemption date in accordance with the
terms of the indenture and those debt securities.



    This trust may only be established if, among other things:



    - the Company has delivered to the trustee a legal opinion to the effect
      that the holders of the debt securities will not recognize income, gain or
      loss for United States federal income tax purposes as a result of such
      legal defeasance or covenant defeasance and will be subject to United
      States federal income tax on the same amounts, in the same manner and at
      the same times as would have been the case if such legal defeasance or
      covenant defeasance had not occurred, and such legal opinion, in the case
      of legal defeasance, must refer to and be based upon a ruling of the
      Internal Revenue Service or a change in applicable United States federal,
      income tax law occurring after the date of the indenture;



    - such legal defeasance or covenant defeasance will not result in a breach
      or violation of, or constitute a default under, the indenture or any other
      material agreement or instrument to which the Company is a party or by
      which it is bound; and


                                       28
<PAGE>

    - no event of default or event which with notice or lapse of time or both
      would become an event of default with respect to the debt securities shall
      have occurred and shall be continuing on the date of, or, solely in the
      case of events of default due to certain events of bankruptcy, insolvency,
      or reorganization, during the period ending on the 91st day after the date
      of, such deposit into trust.



    "Government Obligations" means securities which are:



    - direct obligations of the United States of America, for the payment of
      which obligations its full faith and credit is pledged; or



    - obligations of a person controlled or supervised by and acting as an
      agency or instrumentality of the United States of America, the payment of
      which is unconditionally guaranteed as a full faith and credit obligation
      by the United States of America and which, in either of the above cases,
      are not callable or redeemable at the option of the issuer thereof and
      also includes a depository receipt issued by a bank or trust company as
      custodian with respect to any such Government Obligation held by such
      custodian for the account of the holder of a depository receipt, provided
      that (except as provided by law) such custodian is not authorized to make
      any amount received by the custodian.



SUBORDINATION



    The applicable prospectus supplement will set forth the terms and
conditions, if any, upon which the debt securities are subordinated to other
indebtedness of the Company. Such terms will include a description of the
indebtedness ranking senior to the debt securities, the restrictions on payments
to the holders of such debt securities while a default with respect to such
senior indebtedness is continuing, the restrictions, if any, on payments to the
holders of such debt securities following an event of default, and provisions
requiring holders of such debt securities to remit certain payment to holders of
senior indebtedness.



WARRANTS TO PURCHASE DEBT SECURITIES



    The following statements with respect to the debt warrants are summaries of,
and subject to, the detailed provisions of a warrant agreement to be entered
into by us and a warrant agent to be selected at the time of issue.



GENERAL



    The debt warrants, evidenced by warrant certificates, may be issued under
the debt warrant agreement independently or together with any debt securities
offered by any prospectus supplement and may be attached to or separate from
such debt securities. If debt warrants are offered, the prospectus supplement
will describe the terms of the warrants, including the following:



    - the offering price, if any;



    - the designation, aggregate principal amount and terms of the debt
      securities purchasable upon exercise of the warrants;



    - if applicable, the designation and terms of the debt securities with which
      the debt warrants are issued and the number of debt warrants issued with
      each such debt security;



    - if applicable, the date on and after which the debt warrants and the
      related debt securities will be separately transferable;



    - the principal amount of debt securities purchasable upon exercise of one
      debt warrant and the price at which such principal amount of debt
      securities may be purchased upon exercise;


                                       29
<PAGE>

    - the date on which the right to exercise the debt warrants shall commence
      and the date on which such right shall expire;



    - Federal income tax consequences;



    - whether the warrants represented by the debt warrant certificates will be
      issued in registered or bearer form;



    - the currency, currencies or currency units in which the offering price, if
      any, and exercise price are payable;



    - the antidilution provisions of the debt warrants; and



    - any other terms of the debt warrants.



    Debt warrant certificates may be exchanged for new debt warrant certificates
of different denominations and may (if in registered form) be presented for
registration of transfer at the corporate trust office of the debt warrant
agent, which will be listed in the prospectus supplement, or at such other
office as may be set forth therein. Warrantholders do not have any of the rights
of holders of debt securities (except to the extent that the consent of
warrantholders may be required for certain modifications of the terms of an
indenture and the series of debt securities issuable upon exercise of the debt
warrants) and are not entitled to payments of principal of and interest, if any,
on the debt securities.



EXERCISE OF DEBT WARRANTS



    Debt warrants may be exercised by surrendering the debt warrant certificate
at the corporate trust office of the debt warrant agent, with the form of
election to purchase on the reverse side of the debt warrant certificate
properly completed and executed, and by payment in full of the exercise price,
as set forth in the prospectus supplement. Upon the exercise of debt warrants,
the debt warrant agent will, as soon as practicable, deliver the debt securities
in authorized denominations in accordance with the instructions of the
exercising warrantholder and at the sole cost and risk of such holder. If less
than all of the debt warrants evidenced by the warrant certificate are
exercised, a new debt warrant certificate will be issued for the remaining
amount of debt warrants.


                                       30
<PAGE>

                              PLAN OF DISTRIBUTION



    We may sell securities offered pursuant to any applicable prospectus
supplement directly to one or more purchasers or though agents or underwriters.
We may sell securities offered pursuant to any applicable prospectus supplement
in at-the-market equity offerings or on a negotiated or competitive bid basis
through underwriters or dealers or directly to other purchasers or through
agents. We will name any underwriter or agent involved in the offer and sale of
the securities in the applicable prospectus supplement.



    We may distribute the securities from time to time in one or more
transactions:



    - at a fixed price or prices, which may be changed;



    - at market prices prevailing at the time of sale;



    - at prices related to prevailing market prices; or



    - at negotiated prices.



    We also may, from time to time, authorize underwriters acting as our agents
to offer and sell securities upon the terms and conditions as set forth in the
applicable prospectus supplement. In connection with the sale of the securities,
underwriters may be deemed to have received compensation from us in the form of
underwriting discounts or commissions and may also receive commissions from
purchasers of securities for whom they may act as agent.



    Underwriters may sell the securities to or through dealers, and dealers may
receive compensation in the form of discounts, concessions or commissions from
the underwriters and/or commissions from the purchasers for whom they may act as
agent.



    We will describe in the applicable prospectus supplement any underwriting
compensation we pay to underwriters or agents in connection with the offering of
the securities, and any discounts, concessions or commissions allowed by
underwriters to participating dealers. Dealers and agents participating in the
distribution of the securities may be deemed to be underwriters, and any
discounts and commissions received by them and any profit realized by them on
resale of the securities may be deemed to be underwriting discounts and
commissions. We may enter into agreements to indemnify underwriters, dealers and
agents against certain civil liabilities, including liabilities under the
Securities Act, and to reimburse these persons for certain expenses. We will
describe any indemnification agreements in the applicable prospectus supplement.



    Unless we specify otherwise in the related prospectus supplement, each
series of securities offered will be a new issue with no established trading
market, other than the common stock which is listed on the Nasdaq National
Market System. Any shares of common stock sold pursuant to a prospectus
supplement may be listed on the Nasdaq National Market System, subject to
official notice of issuance. We may elect to list any series of preferred stock
and any series of debt securities, depository shares or warrants on any
exchange, but we are not obligated to do so. It is possible that one or more
underwriters may make a market in a series of offered securities, but will not
be obligated to do so and may discontinue any market making at any time without
notice. Therefore, no assurance can be given as to the liquidity of the trading
market for the securities.



    If indicated in the applicable prospectus supplement, we may authorize
dealers acting as our agents to solicit offers by certain institutions to
purchase the securities from us at the public offering price set forth in the
prospectus supplement pursuant to delayed delivery contracts providing for
payment and delivery on the date or dates stated in the prospectus supplement.
We may make delayed delivery with various institutions, including commercial and
savings banks, insurance companies,


                                       31
<PAGE>

pension funds, investment companies and educational and charitable institutions.
Delayed delivery contracts will not be subject to any conditions except:



    - the purchase by an institution of the securities covered by its delayed
      delivery contracts shall not at the time of delivery be prohibited under
      the laws of any jurisdiction in the United States to which the institution
      is subject; and



    - if the securities are sold to underwriters, we shall have sold to the
      underwriters the total principal amount of the offered securities less the
      principal amount covered by the delayed delivery contracts.



    To facilitate the offering of the securities, certain persons participating
in the offering may engage in transactions that stabilize, maintain, or
otherwise affect the price of the securities. This may include over-allotments
or short sales of the securities, which involves the sale by persons
participating in the offering of more securities than we sold to them. In these
circumstances, these persons would cover the over-allotments or short positions
by making purchases in the open market or by exercising their over-allotment
option. In addition, these persons may stabilize or maintain the price of the
debt securities by bidding for or purchasing debt securities in the open market
or by imposing penalty bids, whereby selling concessions allowed to dealers
participating in the offering may be reclaimed if securities sold by them are
repurchased in connection with stabilization transactions. The effect of these
transactions may be to stabilize or maintain the market price of the securities
at a level above that which might otherwise prevail in the open market. These
transactions may be discontinued at any time.



    Certain of the underwriters and their affiliates may be customers of, engage
in transactions with and perform services for, us in the ordinary course of
business.



                                 LEGAL MATTERS



    The validity of the Securities offered hereby will be passed upon for us by
Crowley, Haughey, Hanson, Toole & Dietrich, P.L.L.P., Kalispell, Montana.



                                    EXPERTS





    The financial statements incorporated in this Prospectus by reference to our
Annual Report on Form 10-K for the year ended September 30, 1999 have been so
incorporated in reliance on the report of PricewaterhouseCoopers LLP,
independent accountants, given on the authority of said firm as experts in
auditing and accounting.


                                       32
<PAGE>
                                    PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

    The following table sets forth the costs and expenses, other than
underwriting discounts and commissions, payable by Semitool, Inc. (the
"Company") in connection with the sale of common stock being registered. All
amounts are estimates except the SEC registration fee and the NASD filing fee.


<TABLE>
<S>                                                           <C>
SEC registration fee........................................  $ 19,800
NASD filing fee.............................................     8,987
Nasdaq National Market listing fee..........................    17,500
Printing and engraving costs................................   135,000
Legal fees and expenses.....................................   250,000
Accounting fees and expenses................................   150,000
Blue sky fees and expenses..................................     5,000
Transfer agent and registrar fees and expenses..............     5,000
Miscellaneous expenses......................................     8,713
                                                              --------
  Total.....................................................  $600,000
                                                              ========
</TABLE>


ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS

    Sections 35-1-451 through 35-1-459 of the Montana Code Annotated authorize a
court to award, or a corporation to provide, indemnification to directors and
officers on terms sufficiently broad to permit indemnification under certain
circumstances for liabilities arising under the Securities Act of 1933, as
amended. Section 35-1-452 of the Montana Code Annotated authorizes a corporation
to indemnify a director against liability incurred because he is or was a
director of the registrant, provided that certain standards are met, except in
connection with a proceeding by or in the right of the corporation in which the
director is adjudged liable to the corporation or in connection with any other
proceeding in which the director is adjudged liable on that basis that personal
benefit was improperly received by the director. Article VII, Section B of the
Company's Articles of Incorporation provides for indemnification of the
Company's directors, officers, employees and agents to an extent not
inconsistent with Montana law.

    Directors of the Company may also be indemnified pursuant to a liability
insurance policy maintained by the Company for such purposes. The Underwriting
Agreement (Exhibit 1.1 hereto) provides for indemnification by the underwriters
of the registrant and its executive officers and directors, and by the
registrant of the underwriters, for certain liabilities, including liabilities
arising under the Securities Act, in connection with matters specifically
provided by the underwriters for inclusion in this Registration Statement.

    Section 35-1-216(2)(d) authorizes a corporation to include in its articles
of incorporation a provision eliminating or limiting the liability of a director
to the corporation or its shareholders for money damages for any actions or
omissions by a director, except liability for the amount of a financial benefit
received by a director to which the director is not entitled, an intentional
infliction of harm on the corporation or the shareholders, an intentional
violation of criminal law, or if the director participates in making an unlawful
distribution. Article VII, Section A of the Company's Articles of Incorporation
contains provisions implementing, to the fullest extent permitted by Montana
law, such limitations on a director's liability to the registrant and its
shareholders.

    The Company entered into agreements with its directors and executive
officers that require the Company to indemnify such persons against expenses,
judgments, fines, settlements and other amounts actually and reasonably incurred
(including expenses of a derivative action) in connection with any

                                      II-1
<PAGE>
proceeding, whether actual or threatened, to which any such person may be made a
party by reason of the fact that such person is or was a director or officer of
the Company or any of its affiliated enterprises, provided such person acted in
good faith and in a manner such person reasonably believed to be in or not
opposed to the best interests of the Company and also sets forth certain
procedures that will apply in the event of a claim for indemnification
thereunder.

ITEM 16. EXHIBITS

    The Exhibits are as set forth on the Exhibit Index hereto.

ITEM 17. UNDERTAKINGS

    Insofar as indemnification by the Company for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Company pursuant to the provisions referenced in Item 15 of this
Registration Statement or otherwise, the Company has been advised that in the
opinion of the Securities and Exchange Commission such indemnification is
against public policy as expressed in the Securities Act, and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the Company of expenses incurred or paid
by a director, officer, or controlling person of the Company in the successful
defense of any action, suit or proceeding) is asserted by such director, officer
or controlling person in connection with the securities being registered
hereunder, the Company will, unless in the opinion of its counsel the matter has
been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

    The undersigned Company hereby undertakes that:

    (1) For purposes of determining any liability under the Securities Act, the
information omitted from the form of prospectus filed as part of this
Registration Statement in reliance upon Rule 430A and contained in a form of
prospectus filed by the Company pursuant to Rule 424(b)(1) or (4) or 497(h)
under the Securities Act shall be deemed to be part of this Registration
Statement as of the time it was declared effective.

    (2) For the purpose of determining any liability under the Securities Act,
each post-effective amendment that contains a form of prospectus shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial BONA FIDE offering thereof.

                                      II-2
<PAGE>
                                   SIGNATURES


    Pursuant to the requirements of the Securities Act, the Company certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-3 and has duly caused this Amendment No. 3 to the
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Kalispell, State of Montana, on September 1,
2000.


<TABLE>
<S>                                                    <C>  <C>
                                                       SEMITOOL, INC.

                                                       By   /s/ RAYMON F. THOMPSON
                                                            -----------------------------------------
                                                            Raymon F. Thompson
                                                            CHAIRMAN OF THE BOARD, PRESIDENT AND CHIEF
                                                            EXECUTIVE OFFICER
</TABLE>


    Pursuant to the requirements of the Securities Act, this Amendment No. 3 to
the Registration Statement has been signed by the following persons in the
capacities and on the dates indicated:



<TABLE>
<CAPTION>
                      SIGNATURE                                   TITLE                    DATE
                      ---------                                   -----                    ----
<C>                                                    <S>                          <C>
               /s/ RAYMON F. THOMPSON                  Chairman of the Board,
     -------------------------------------------       President and Chief          September 1, 2000
                (Raymon F. Thompson)                   Executive Officer

               /s/ WILLIAM A. FREEMAN
     -------------------------------------------       Senior Vice President and    September 1, 2000
                (William A. Freeman)                   Chief Financial Officer

                 /s/ LARRY A. VIANO                    Controller, Treasurer,
     -------------------------------------------       Secretary, and Principal     September 1, 2000
                  (Larry A. Viano)                     Accounting Officer

                /s/ HOWARD E. BATEMAN
     -------------------------------------------       Director                     September 1, 2000
                 (Howard E. Bateman)

                /s/ RICHARD A. DASEN
     -------------------------------------------       Director                     September 1, 2000
                 (Richard A. Dasen)

                                                       Director and Senior Vice
               /s/ TIMOTHY C. DODKIN*                  President, Managing
     -------------------------------------------       Director, Semitool Europe,   September 1, 2000
                 (Timothy C. Dodkin)                   Ltd.

               /s/ DANIEL J. EIGEMAN*
     -------------------------------------------       Director                     September 1, 2000
                 (Daniel J. Eigeman)
</TABLE>


<TABLE>
<S>   <C>
*By:                /s/ RAYMON F. THOMPSON
           ----------------------------------------
                      Raymon F. Thompson
                       ATTORNEY-IN-FACT
</TABLE>

                                      II-3
<PAGE>
                                 EXHIBIT INDEX


<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER
---------------------
<C>                     <S>
         4.1            Form of Indenture (1)

         4.2            Form of Certificate of Designation (1)

         4.3            Form of Warrant (1)

         4.4            Form of Deposit Agreement (1)

         4.5            Form of Note (1)

         5.1            Opinion of Crowley, Haughey, Hanson, Toole & Dietrich,
                        P.L.L.P. (1)

        23.1            Consent of PricewaterhouseCoopers LLP

        24.1*           Power of Attorney (included on signature page to
                        Registration Statement)

        25.1            Statement of Eligibility of Trustee on Form T-1 (1)

        27.1            Financial Data Schedule (2)

        99.2            Amended and Restated Semitool, Inc. 1994 Stock Option Plan
                        (3)
</TABLE>


------------

*   Previously provided.


(1) To be filed by amendment or incorporated by reference in connection with the
    offering of the applicable securities.



(2) Incorporated herein by reference to the identically numbered exhibit to the
    Company's Annual Report on Form 10-K, date of report September 30, 1999.



(3) Incorporated herein by reference to the identically numbered exhibit to the
    Company's Quarterly Report on Form 10-Q, date of report March 31, 1998.