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                                                                    EXHIBIT 10.1

                              MKS INSTRUMENTS, INC.

                            2004 STOCK INCENTIVE PLAN

1.    Purpose

      The purpose of this 2004 Stock Incentive Plan (the "Plan") of MKS
Instruments, Inc., a Massachusetts corporation (the "Company"), is to advance
the interests of the Company's stockholders by enhancing the Company's ability
to attract, retain and motivate persons who are expected to make important
contributions to the Company and by providing such persons with equity ownership
opportunities and performance-based incentives that are intended to better align
their interests with those of the Company's stockholders. Except where the
context otherwise requires, the term "Company" shall include any of the
Company's present or future subsidiary corporations as defined in Section 424(f)
of the Internal Revenue Code of 1986, as amended, and any regulations
promulgated thereunder (the "Code") and any other business venture (including,
without limitation, joint venture or limited liability company) in which the
Company has a controlling interest, as determined by the Board of Directors of
the Company (the "Board").

2.    Eligibility

      All of the Company's employees, officers, directors, consultants and
advisors are eligible to receive options, restricted stock awards, stock
appreciation rights and other stock-based awards (each, an "Award") under the
Plan. Each person who receives an Award under the Plan is deemed a
"Participant".

3.    Administration and Delegation

      (a) Administration by Board of Directors. The Plan will be administered by
the Board. The Board shall have authority to grant Awards and to adopt, amend
and repeal such administrative rules, guidelines and practices relating to the
Plan as it shall deem advisable. The Board may correct any defect, supply any
omission or reconcile any inconsistency in the Plan or any Award in the manner
and to the extent it shall deem expedient to carry the Plan into effect and it
shall be the sole and final judge of such expediency. All decisions by the Board
shall be made in the Board's sole discretion and shall be final and binding on
all persons having or claiming any interest in the Plan or in any Award. No
director or person acting pursuant to the authority delegated by the Board shall
be liable for any action or determination relating to or under the Plan made in
good faith.

      (b) Appointment of Committees.

            (1) To the extent permitted by applicable law, the Board may
delegate any or all of its powers under the Plan to one or more committees or
subcommittees of the Board (a "Committee"). During such time as the common
stock, no par value per share, of the Company (the "Common Stock") is registered
under the Securities Exchange Act of 1934 (the "Exchange Act"), the Board shall
appoint one such Committee of not less than two members, each member of which
shall be an "outside director" within the meaning of Section 162(m) of the Code
and a "non-employee director" as defined in Rule 16b-3 promulgated under the
Exchange Act.
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            (2) To the extent permitted by applicable law, the Board may
delegate to one or more officers of the Company, who, if required by law, are
also members of the Board, the power to make Awards and exercise such other
powers under the Plan as the Board shall determine, provided that the Board
shall fix the maximum number of shares subject to Awards to be made by any such
person and such other terms as the Board may determine are appropriate.

            (3) All references in the Plan to the "Board" shall mean the Board,
a Committee of the Board or any person described in subsection (2) above, to the
extent that the Board's powers or authority under the Plan have been delegated
to such Committee or person.

4.    Stock Available for Awards

      (a) Number of Shares. Subject to adjustment under Section 9, the number of
shares of Common Stock available for Awards under the Plan: (i) shall annually
increase by 5% of the total shares of the Company's outstanding Common Stock on
January 1 of each year; and (ii) in the event of an increase in the total shares
of the Company's Common Stock after January 1 of any such year in connection
with the acquisition of any corporation, partnership or other business entity by
the Company (whether by merger, stock purchase or otherwise), shall increase by
5% of such increased amount. Such increases shall occur until such time as the
aggregate number of shares of Common Stock which may be issued under the Plan is
15,000,000 shares, subject to adjustment under Section 9. If any Award expires
or is terminated, surrendered or canceled without having been fully exercised or
is forfeited in whole or in part (including as the result of shares of Common
Stock subject to such Award being repurchased by the Company at the original
issuance price pursuant to a contractual repurchase right) or results in any
Common Stock not being issued, the unused Common Stock covered by such Award
shall again be available for the grant of Awards under the Plan, subject,
however, in the case of Incentive Stock Options (as hereinafter defined), to any
limitations under the Code. Shares issued under the Plan may consist in whole or
in part of authorized but unissued shares or treasury shares.

      (b) Per-Participant Limit. Subject to adjustment under Section 9, the
maximum number of shares of Common Stock with respect to which Awards may be
granted to any Participant under the Plan shall be 900,000 per calendar year.
The per-Participant limit described in this Section 4(b) shall be construed and
applied consistently with Section 162(m) of the Code.

5.    Stock Options

      (a) General. The Board may grant options to purchase Common Stock (each,
an "Option") and determine the number of shares of Common Stock to be covered by
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option, including conditions
relating to applicable federal or state securities laws, as it considers
necessary or advisable. An Option which is not intended to be an Incentive Stock
Option (as hereinafter defined) shall be designated a "Nonstatutory Stock
Option".

      (b) Incentive Stock Options. An Option that the Board intends to be an
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
Stock Option") shall only be granted to employees of MKS Instruments, Inc., any
of MKS Instruments, Inc.'s present or future subsidiary corporations as defined
in Section 424(f) of the Code, and any other entities the


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employees of which are eligible to receive Incentive Stock Options under the
Code, and shall be subject to and shall be construed consistently with the
requirements of Section 422 of the Code. The Company shall have no liability to
a Participant, or any other party, if an Option (or any part thereof) that is
intended to be an Incentive Stock Option is not an Incentive Stock Option or for
any action taken by the Board pursuant to Section 10(f), including without
limitation the conversion of an Incentive Stock Option to a Nonstatutory Stock
Option.

      (c) Exercise Price. The Board shall establish the exercise price of each
Option and specify such exercise price in the applicable option agreement.

      (d) Duration of Options. Each Option shall be exercisable at such times
and subject to such terms and conditions as the Board may specify in the
applicable option agreement; provided, however, that no Option will be granted
for a term in excess of 10 years.

      (e) Exercise of Option. Options may be exercised by delivery to the
Company of a written notice of exercise signed by the proper person or by any
other form of notice (including electronic notice) approved by the Board
together with payment in full as specified in Section 5(f) for the number of
shares for which the Option is exercised.

      (f) Payment Upon Exercise. Common Stock purchased upon the exercise of an
Option granted under the Plan shall be paid for as follows:

(1) in cash or by check, payable to the order of the Company;

(2) except as the Board may otherwise provide in an option agreement, by (i)
delivery of an irrevocable and unconditional undertaking by a creditworthy
broker to deliver promptly to the Company sufficient funds to pay the exercise
price and any required tax withholding or (ii) delivery by the Participant to
the Company of a copy of irrevocable and unconditional instructions to a
creditworthy broker to deliver promptly to the Company cash or a check
sufficient to pay the exercise price and any required tax withholding;

(3) to the extent permitted by applicable law and by the Board, by (i) delivery
of a promissory note of the Participant to the Company on terms determined by
the Board, or (ii) payment of such other lawful consideration as the Board may
determine; or

(4) by any combination of the above permitted forms of payment.

6.    Stock Appreciation Rights.

      (a) Nature of Stock Appreciation Rights. A Stock Appreciation Right, or
SAR, is an Award entitling the holder on exercise to receive an amount in cash
or Common Stock or a combination thereof (such form to be determined by the
Board) determined in whole or in part by reference to appreciation, from and
after the date of grant, in the fair market value of a share of Common Stock.
SARs may be based solely on appreciation in the fair market value of Common
Stock or on a comparison of such appreciation with some other measure of market
growth such as (but not limited to) appreciation in a recognized market index.
The date as of which such appreciation or other measure is determined shall be
the exercise date unless another date is specified by the Board in the SAR
Award.


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      (b) Grants. Stock Appreciation Rights may be granted in tandem with, or
independently of, Options granted under the Plan.

      (c) Exercise. Any exercise of a Stock Appreciation Right must be in
writing, signed by the proper person and delivered or mailed to the Company,
accompanied by any other documents required by the Board.

7.    Restricted Stock.

      (a) Grants. The Board may grant Awards entitling recipients to acquire
shares of Common Stock, subject to the right of the Company to repurchase all or
part of such shares at their issue price or other stated or formula price (or to
require forfeiture of such shares if issued at no cost) from the recipient in
the event that conditions specified by the Board in the applicable Award are not
satisfied prior to the end of the applicable restriction period or periods
established by the Board for such Award (each, a "Restricted Stock Award").

      (b) Terms and Conditions. The Board shall determine the terms and
conditions of a Restricted Stock Award, including the conditions for repurchase
(or forfeiture) and the issue price, if any.

      (c) Stock Certificates. Any stock certificates issued in respect of a
Restricted Stock Award shall be registered in the name of the Participant and,
unless otherwise determined by the Board, deposited by the Participant, together
with a stock power endorsed in blank, with the Company (or its designee). At the
expiration of the applicable restriction periods, the Company (or such designee)
shall deliver the certificates no longer subject to such restrictions to the
Participant or if the Participant has died, to the beneficiary designated, in a
manner determined by the Board, by a Participant to receive amounts due or
exercise rights of the Participant in the event of the Participant's death (the
"Designated Beneficiary"). In the absence of an effective designation by a
Participant, "Designated Beneficiary" shall mean the Participant's estate.

      (d) Deferred Delivery of Shares. The Board may, at the time any Restricted
Stock Award is granted, provide that, at the time Common Stock would otherwise
be delivered pursuant to the Award, the Participant shall instead receive an
instrument evidencing the right to future delivery of Common Stock at such time
or times, and on such conditions, as the Board shall specify. The Board may at
any time accelerate the time at which delivery of all or any part of the Common
Stock shall take place.

8.    Other Stock-Based Awards.

      Other Awards of shares of Common Stock, and other Awards that are valued
in whole or in part by reference to, or are otherwise based on, shares of Common
Stock or other property, may be granted hereunder to Participants ("Other Stock
Unit Awards"), including without limitation Awards entitling recipients to
receive shares of Common Stock to be delivered in the future. Such Other Stock
Unit Awards shall also be available as a form of payment in the settlement of
other Awards granted under the Plan or as payment in lieu of compensation to
which a Participant is otherwise entitled. Other Stock Unit Awards may be paid
in shares of Common Stock or cash, as the Board shall determine. Subject to the
provisions of the Plan, the Board shall determine the conditions of each Other
Stock Unit Award, including any purchase


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price applicable thereto. At the time any Award is granted, the Board may
provide that, at the time Common Stock would otherwise be delivered pursuant to
the Award, the Participant will instead receive an instrument evidencing the
Participant's right to future delivery of the Common Stock.

9.    Adjustments for Changes in Common Stock and Certain Other Events.

      (a) Changes in Capitalization. In the event of any stock split, reverse
stock split, stock dividend, recapitalization, combination of shares,
reclassification of shares, spin-off or other similar change in capitalization
or event, or any distribution to holders of Common Stock other than an ordinary
cash dividend, (i) the number and class of securities available under this Plan,
(ii) the per-Participant limit set forth in Section 4(b), (iii) the number and
class of securities and exercise price per share of each outstanding Option,
(iv) the repurchase price per share subject to each outstanding Restricted Stock
Award and (v) the share- and per-share-related provisions of each outstanding
Stock Appreciation Right and Other Stock Unit Award, shall be appropriately
adjusted by the Company (or substituted Awards may be made, if applicable) to
the extent determined by the Board.

      (b) Reorganization Events.

(1) Definition. A "Reorganization Event" shall mean: (a) any merger or
consolidation of the Company with or into another entity as a result of which
all of the Common Stock of the Company is converted into or exchanged for the
right to receive cash, securities or other property, (b) any exchange of all of
the Common Stock of the Company for cash, securities or other property pursuant
to a share exchange transaction or (c) any liquidation or dissolution of the
Company.

(2) Consequences of a Reorganization Event on Awards Other than Restricted Stock
Awards. In connection with a Reorganization Event, the Board shall take any one
or more of the following actions as to all or any outstanding Awards on such
terms as the Board determines: (i) provide that Awards shall be assumed, or
substantially equivalent Awards shall be substituted, by the acquiring or
succeeding corporation (or an affiliate thereof), (ii) upon written notice to a
Participant, provide that the Participant's unexercised Options or other
unexercised Awards shall become exercisable in full and will terminate
immediately prior to the consummation of such Reorganization Event unless
exercised by the Participant within a specified period following the date of
such notice, (iii) provide that outstanding Awards shall become realizable or
deliverable, or restrictions applicable to an Award shall lapse, in whole or in
part prior to or upon such Reorganization Event, (iv) in the event of a
Reorganization Event under the terms of which holders of Common Stock will
receive upon consummation thereof a cash payment for each share surrendered in
the Reorganization Event (the "Acquisition Price"), make or provide for a cash
payment to a Participant equal to (A) the Acquisition Price times the number of
shares of Common Stock subject to the Participant's Options or other Awards (to
the extent the exercise price does not exceed the Acquisition Price) minus (B)
the aggregate exercise price of all such outstanding Options or other Awards, in
exchange for the termination of such Options or other Awards, (v) provide that,
in connection with a liquidation or dissolution of the Company, Awards shall
convert into the right to receive liquidation proceeds (if applicable, net of
the exercise price thereof) and (vi) any combination of the foregoing.


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            For purposes of clause (i) above, an Option shall be considered
assumed if, following consummation of the Reorganization Event, the Option
confers the right to purchase, for each share of Common Stock subject to the
Option immediately prior to the consummation of the Reorganization Event, the
consideration (whether cash, securities or other property) received as a result
of the Reorganization Event by holders of Common Stock for each share of Common
Stock held immediately prior to the consummation of the Reorganization Event
(and if holders were offered a choice of consideration, the type of
consideration chosen by the holders of a majority of the outstanding shares of
Common Stock); provided, however, that if the consideration received as a result
of the Reorganization Event is not solely common stock of the acquiring or
succeeding corporation (or an affiliate thereof), the Company may, with the
consent of the acquiring or succeeding corporation, provide for the
consideration to be received upon the exercise of Options to consist solely of
common stock of the acquiring or succeeding corporation (or an affiliate
thereof) equivalent in fair market value to the per share consideration received
by holders of outstanding shares of Common Stock as a result of the
Reorganization Event.

            To the extent all or any portion of an Option becomes exercisable
solely as a result of clause (ii) above, the Board may provide that upon
exercise of such Option the Participant shall receive shares subject to a right
of repurchase by the Company or its successor at the Option exercise price; such
repurchase right (x) shall lapse at the same rate as the Option would have
become exercisable under its terms and (y) shall not apply to any shares subject
to the Option that were exercisable under its terms without regard to clause
(ii) above.

(3) Consequences of a Reorganization Event on Restricted Stock Awards. Upon the
occurrence of a Reorganization Event other than a liquidation or dissolution of
the Company, the repurchase and other rights of the Company under each
outstanding Restricted Stock Award shall inure to the benefit of the Company's
successor and shall apply to the cash, securities or other property which the
Common Stock was converted into or exchanged for pursuant to such Reorganization
Event in the same manner and to the same extent as they applied to the Common
Stock subject to such Restricted Stock Award. Upon the occurrence of a
Reorganization Event involving the liquidation or dissolution of the Company,
except to the extent specifically provided to the contrary in the instrument
evidencing any Restricted Stock Award or any other agreement between a
Participant and the Company, all restrictions and conditions on all Restricted
Stock Awards then outstanding shall automatically be deemed terminated or
satisfied.

10.   General Provisions Applicable to Awards

      (a) Transferability of Awards. Except as the Board may otherwise determine
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution or, other than in the case of an Incentive Stock Option, pursuant
to a qualified domestic relations order, and, during the life of the
Participant, shall be exercisable only by the Participant. References to a
Participant, to the extent relevant in the context, shall include references to
authorized transferees.

      (b) Documentation. Each Award shall be evidenced in such form (written,
electronic or otherwise) as the Board shall determine. Each Award may contain
terms and conditions in addition to those set forth in the Plan.


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      (c) Board Discretion. Except as otherwise provided by the Plan, each Award
may be made alone or in addition or in relation to any other Award. The terms of
each Award need not be identical, and the Board need not treat Participants
uniformly.

      (d) Termination of Status. The Board shall determine the effect on an
Award of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, or the Participant's legal
representative, conservator, guardian or Designated Beneficiary, may exercise
rights under the Award.

      (e) Withholding. Each Participant shall pay to the Company, or make
provision satisfactory to the Company for payment of, any taxes required by law
to be withheld in connection with an Award to such Participant. The Company may,
to the extent permitted by law, deduct any such tax obligations from any payment
of any kind otherwise due to a Participant.

      (f) Amendment of Award. The Board may amend, modify or terminate any
outstanding Award, including but not limited to, substituting therefor another
Award of the same or a different type, changing the date of exercise or
realization, and converting an Incentive Stock Option to a Nonstatutory Stock
Option, provided that the Participant's consent to such action shall be required
unless the Board determines that the action, taking into account any related
action, would not materially and adversely affect the Participant.

      (g) Conditions on Delivery of Stock. The Company will not be obligated to
deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (i) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (ii) in the opinion of the Company's counsel, all other legal matters
in connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (iii) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations.

      (h) Acceleration. The Board may at any time provide that any Award shall
become immediately exercisable in full or in part, free of some or all
restrictions or conditions, or otherwise realizable in full or in part, as the
case may be.

11.   Miscellaneous

      (a) No Right To Employment or Other Status. No person shall have any claim
or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan, except as expressly provided in the
applicable Award.

      (b) No Rights As Stockholder. Subject to the provisions of the applicable
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any


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shares of Common Stock to be distributed with respect to an Award until becoming
the record holder of such shares. Notwithstanding the foregoing, in the event
the Company effects a split of the Common Stock by means of a stock dividend and
the exercise price of and the number of shares subject to such Option are
adjusted as of the date of the distribution of the dividend (rather than as of
the record date for such dividend), then an optionee who exercises an Option
between the record date and the distribution date for such stock dividend shall
be entitled to receive, on the distribution date, the stock dividend with
respect to the shares of Common Stock acquired upon such Option exercise,
notwithstanding the fact that such shares were not outstanding as of the close
of business on the record date for such stock dividend.

      (c) Effective Date and Term of Plan. The Plan shall become effective on
the date on which it is adopted by the Board, but no Award may be granted unless
and until the Plan has been approved by the Company's stockholders. No Awards
shall be granted under the Plan after the completion of 10 years from the
earlier of (i) the date on which the Plan was adopted by the Board or (ii) the
date the Plan was approved by the Company's stockholders, but Awards previously
granted may extend beyond that date.

      (d) Amendment of Plan. The Board may amend, suspend or terminate the Plan
or any portion thereof at any time; provided that, to the extent determined by
the Board, no amendment requiring stockholder approval under any applicable
legal, regulatory or listing requirement shall become effective until such
stockholder approval is obtained. No Award shall be made that is conditioned
upon stockholder approval of any amendment to the Plan.

      (e) Provisions for Foreign Participants. The Board may modify Awards or
Options granted to Participants who are foreign nationals or employed outside
the United States or establish subplans or procedures under the Plan to
recognize differences in laws, rules, regulations or customs of such foreign
jurisdictions with respect to tax, securities, currency, employee benefit or
other matters.

      (f) Governing Law. The provisions of the Plan and all Awards made
hereunder shall be governed by and interpreted in accordance with the laws of
the Commonwealth of Massachusetts, without regard to any applicable conflicts of
law.

                                        As approved by the Board of
                                        Directors on March 4, 2004
                                        and by the stockholders on
                                        May 13, 2004

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