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                                                                     Exhibit 4.1



                                   ATMI, INC.

                      5.25% CONVERTIBLE SUBORDINATED NOTES
                              DUE NOVEMBER 15, 2006


                          REGISTRATION RIGHTS AGREEMENT

                                                               November 13, 2001
Goldman, Sachs & Co.,
Merrill Lynch Pierce Fenner & Smith Incorporated
As representatives of the several Purchasers
   named in Schedule I to the Purchase Agreement
c/o Goldman, Sachs & Co.
85 Broad Street
New York, New York 10004

Ladies and Gentlemen:

         ATMI, Inc., a Delaware corporation (the "Company"), proposes to issue
and sell to the Purchasers (as defined herein) upon the terms set forth in the
Purchase Agreement (as defined herein) its 5.25% Convertible Subordinated Notes
Due November 15, 2006 (the "Securities"). As an inducement to the Purchasers to
enter into the Purchase Agreement and in satisfaction of a condition to the
obligations of the Purchasers thereunder, the Company agrees with the Purchasers
for the benefit of Holders (as defined herein) from time to time of the
Registrable Securities (as defined herein) as follows:

         1.    Definitions.

         (a)   Capitalized terms used herein without definition shall have
the meanings ascribed to them in the Purchase Agreement. As used in this
Agreement, the following defined terms shall have the following meanings:

         "Act" or "Securities Act" means the United States Securities Act of
1933, as amended.

         "Affiliate" of any specified person means any other person which,
directly or indirectly, is in control of, is controlled by, or is under common
control with such specified person. For purposes of this definition, control of
a person means the power, direct or indirect, to direct or cause the direction
of the management and policies of such person whether by contract or
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otherwise; and the terms "controlling" and "controlled" have meanings
correlative to the foregoing.

         "Closing Date" means the First Time of Delivery as defined in the
Purchase Agreement.

         "Commission" means the United States Securities and Exchange
Commission, or any other federal agency at the time administering the Exchange
Act or the Securities Act, whichever is the relevant statute for the particular
purpose.

         "Common Stock" means the Company's common stock, par value $0.01 per
share.

         "DTC" means The Depository Trust Company.

         "Effective Date" has the meaning assigned thereto in Section 2(b)(i)
hereof.

         "Effective Failure" has the meaning assigned thereto in Section 7(b)
hereof.

         "Effectiveness Period" has the meaning assigned thereto in Section
2(b)(i) hereof.

         "Effective Time" means the time at which the Commission declares the
Shelf Registration Statement effective or at which the Shelf Registration
Statement otherwise becomes effective.

         "Electing Holder" has the meaning assigned thereto in Section 3(a)(ii)
hereof.

         "Exchange Act" means the United States Securities Exchange Act of 1934,
as amended.

         "Holder" means, any person that is the record owner of Registrable
Securities (and includes any person that has a beneficial interest in any
Registrable Security in book-entry form).

         "Indenture" means the Indenture, dated as of November 13, 2001, between
the Company and State Street Bank and Trust Company, as Trustee, as amended and
supplemented from time to time in accordance with its terms.

         "Liquidated Damages" has the meaning assigned thereto in Section 7(a)
hereof.

         "Managing Underwriters" means the investment banker or investment
bankers and manager or managers that shall administer an underwritten offering,
if any, conducted pursuant to Section 6 hereof.

         "NASD Rules" means the Rules of the National Association of Securities
Dealers, Inc., as amended from time to time.

         "Notice and Questionnaire" means a Notice of Registration Statement and
Selling Securityholder Questionnaire substantially in the form of Appendix A
hereto.


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<PAGE>
         The term "person" means an individual, partnership, corporation,
limited liability company, trust or unincorporated organization, or a government
or agency or political subdivision thereof.

         "Prospectus" means the prospectus (including, without limitation, any
preliminary prospectus, any final prospectus and any prospectus that discloses
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A under the Act) included in the
Shelf Registration Statement, as amended or supplemented by any prospectus
supplement with respect to the terms of the offering of any portion of the
Registrable Securities covered by the Shelf Registration Statement and by all
other amendments and supplements to such prospectus, including all material
incorporated by reference in such prospectus and all documents filed with the
Commission after the date of such prospectus by the Company under the Exchange
Act and incorporated by reference therein.

         "Purchase Agreement" means the purchase agreement, dated as of November
6, 2001, between the Purchasers and the Company relating to the Securities.

         "Purchasers" means the Purchasers named in Schedule I to the Purchase
Agreement.

         "Registrable Securities" means all or any portion of the Securities
issued from time to time under the Indenture in registered form and the shares
of Common Stock issuable upon conversion or repurchase of such Securities;
provided, however, that a security ceases to be a Registrable Security when it
is no longer a Restricted Security.

         "Registration Default" has the meaning assigned thereto in Section 7(a)
hereof.

         "Restricted Security" means any Security or share of Common Stock
issuable upon conversion or repurchase thereof, except any such Security or
share of Common Stock that (i) has been effectively registered under the
Securities Act and sold in a manner contemplated by the Shelf Registration
Statement, (ii) has been transferred in compliance with Rule 144 under the
Securities Act (or any successor provision thereto) or is transferable pursuant
to paragraph (k) of such Rule 144 (or any successor provision thereto), or (iii)
has otherwise been transferred and a new Security or share of Common Stock not
subject to transfer restrictions under the Securities Act has been delivered by
or on behalf of the Company in accordance with Section 3.5 of the Indenture.

         "Rules and Regulations" means the published rules and regulations of
the Commission promulgated under the Securities Act or the Exchange Act, as in
effect at any relevant time.

         "Shelf Registration" means a registration effected pursuant to Section
2 hereof.

         "Shelf Registration Statement" means a "shelf" registration statement
filed with the Commission under the Securities Act providing for the
registration of, and the sale on a continuous or delayed basis by the Holders
of, all of the Registrable Securities pursuant to Rule 415 under the Securities
Act and/or any similar rule that may be adopted by the Commission,


                                                                             -3-
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filed by the Company pursuant to the provisions of Section 2 of this Agreement,
including the Prospectus contained therein, any amendments and supplements to
such registration statement, including post-effective amendments, and all
exhibits to, and all material incorporated by reference in, such registration
statement.

         "Trust Indenture Act" means the Trust Indenture Act of 1939, or any
successor thereto, and the rules, regulations and forms promulgated thereunder,
as the same shall be amended from time to time.

         The term "underwriter" means any underwriter of Registrable Securities
in connection with an offering thereof under a Shelf Registration Statement.

         (b)   Wherever there is a reference in this Agreement to a
percentage of the "principal amount" of Registrable Securities or to a
percentage of Registrable Securities, Common Stock shall be treated as
representing the principal amount of Securities that was surrendered for
conversion or exchange in order to receive such number of shares of Common
Stock.

         2.    Shelf Registration.

         (a)   The Company shall, no later than 90 calendar days following
the Closing Date, file with the Commission a Shelf Registration Statement
relating to the offer and sale of the Registrable Securities by the Holders from
time to time in accordance with the methods of distribution elected by such
Holders and set forth in such Shelf Registration Statement and, thereafter,
shall use all reasonable efforts to cause such Shelf Registration Statement to
be declared effective under the Act no later than 180 calendar days following
the Closing Date; provided, however, that the Company may, upon written notice
to all Holders, postpone having the Shelf Registration Statement filed or
declared effective for a reasonable period not to exceed 90 days if the Company
possesses material non-public information, the disclosure of which would have a
material adverse effect on the Company and its subsidiaries taken as a whole;
provided, further, however, that no Holder shall be entitled to be named as a
selling securityholder in the Shelf Registration Statement or to use the
Prospectus forming a part thereof for resales of Registrable Securities unless
such Holder is an Electing Holder.

         (b)   The Company shall use all reasonable efforts:

                  (i) to keep the Shelf Registration Statement continuously
         effective in order to permit the Prospectus forming a part thereof to
         be usable by Holders until the earliest of (1) the sale of all
         Registrable Securities registered under the Shelf Registration
         Statement; (2) the expiration of the period referred to in Rule 144(k)
         of the Act with respect to all Registrable Securities held by persons
         that are not Affiliates of the Company; and (3) two years from the date
         (the "Effective Date") of the Effective Time of such Shelf Registration
         Statement (such period being referred to herein as the "Effectiveness
         Period");

                   (ii) after the Effective Time of the Shelf Registration
         Statement, promptly upon the request of any Holder of Registrable
         Securities that is not then an Electing


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         Holder, to take any action reasonably necessary to enable such Holder
         to use the Prospectus forming a part thereof for resales of Registrable
         Securities, including, without limitation, any action necessary to
         identify such Holder as a selling securityholder in the Shelf
         Registration Statement; provided, however, that nothing in this
         subparagraph shall relieve such Holder of the obligation to return a
         completed and signed Notice and Questionnaire to the Company in
         accordance with Section 3(a)(ii) hereof; and

                  (iii) if at any time the Securities, pursuant to Article XII
         of the Indenture, are convertible into securities other than Common
         Stock, to cause, or to cause any successor under the Indenture to
         cause, such securities to be included in the Shelf Registration
         Statement no later than the date on which the Securities may then be
         convertible into such securities.

The Company shall be deemed not to have used all reasonable efforts to keep the
Shelf Registration Statement effective during the requisite period if the
Company voluntarily takes any action that would result in Holders of Registrable
Securities covered thereby not being able to offer and sell any of such
Registrable Securities during that period, unless such action is (A) required by
applicable law and the Company thereafter promptly complies with the
requirements of Section 3(j) below or (B) permitted pursuant to Section 2(c)
below.

         (c)   The Company may suspend the use of the Prospectus for a period
not to exceed 30 days in any 90-day period or an aggregate of 90 days in any
12-month period if the Board of Directors of the Company shall have determined
in good faith that because of valid business reasons (not including avoidance of
the Company's obligations hereunder), including, without limitation, the
acquisition or divestiture of assets or businesses, pending corporate
developments and similar events, it is in the best interests of the Company to
suspend such use, and prior to suspending such use the Company provides the
Holders with written notice of such suspension, which notice need not specify
the nature of the event giving rise to such suspension.

         3.    Registration Procedures. In connection with the Shelf
Registration Statement, the following provisions shall apply:

         (a) (i)    Not less than 30 calendar days prior to the time the Company
intends in good faith to be the Effective Time of the Shelf Registration
Statement, the Company shall mail the Notice and Questionnaire to the Holders of
Registrable Securities. No Holder shall be entitled to be named as a selling
securityholder in the Shelf Registration Statement as of the Effective Time, and
no Holder shall be entitled to use the Prospectus forming a part thereof for
resales of Registrable Securities at any time, unless such Holder has returned a
completed and signed Notice and Questionnaire to the Company by the deadline for
response set forth therein; provided, however, that Holders of Registrable
Securities shall have at least 28 calendar days from the date on which the
Notice and Questionnaire is first mailed to such Holders to return a completed
and signed Notice and Questionnaire to the Company.


                                                                             -5-
<PAGE>
                  (ii) After the Effective Time of the Shelf Registration
         Statement, the Company shall, upon the request of any Holder of
         Registrable Securities that is not then an Electing Holder, as promptly
         as reasonably practicable send a Notice and Questionnaire to such
         Holder. The Company shall not be required to take any action to name
         such Holder as a selling securityholder in the Shelf Registration
         Statement or to enable such Holder to use the Prospectus forming a part
         thereof for resales of Registrable Securities until such Holder has
         returned a completed and signed Notice and Questionnaire to the
         Company. Notwithstanding anything to the contrary in this Agreement,
         (A) the Company may take reasonable steps to aggregate the addition of
         Electing Holders and/or Registrable Securities for purposes of filing
         amendments to the Shelf Registration Statement or supplements to the
         Prospectus so as to reduce the need for multiple amendments or
         supplements, provided that no such actions may delay the filing of an
         amendment or supplement for more than seven business days, and (B)
         commencing six months after the Effective Date of the Shelf
         Registration Statement, the Company shall not be required to prepare
         and file amendments to the Shelf Registration Statement or supplements
         to the Prospectus that are necessary to add Electing Holders and/or
         Registrable Securities to the Shelf Registration Statement more
         frequently than once within any three-month period, the time of such
         filings to within the reasonable discretion of the Company, except that
         the foregoing limitations shall not apply to the Purchasers and except
         that if Goldman, Sachs & Co. advises the Company that this limitation
         would materially impair the liquidity of the Registrable Securities for
         any Electing Holder or group of Electing Holders, then the Company and
         Goldman, Sachs & Co. shall jointly agree in good faith on a more
         frequent schedule for these filings taking into account the then
         relevant circumstances.

                  (iii) The term "Electing Holder" shall mean any Holder of
         Registrable Securities that has returned a completed and signed Notice
         and Questionnaire to the Company in accordance with Section 3(a)(i) or
         3(a)(ii) hereof.

         (b)   The Company shall furnish to each Electing Holder, prior to
the Effective Time, a copy of the Shelf Registration Statement initially filed
with the Commission, and shall furnish to such Electing Holders, prior to the
filing thereof with the Commission, copies of each amendment thereto and each
amendment or supplement, if any, to the Prospectus included therein, and shall
use all reasonable efforts to reflect in each such document, at the Effective
Time or when so filed with the Commission, as the case may be, such comments as
such Holders and their respective counsel reasonably may propose.

         (c) The Company shall promptly take such action as may be necessary so
that (i) each of the Shelf Registration Statement and any amendment thereto and
the Prospectus forming a part thereof and any amendment or supplement thereto
(and each report or other document incorporated therein by reference in each
case) complies in all material respects with the Securities Act and the Exchange
Act and the respective rules and regulations thereunder, (ii) each of the Shelf
Registration Statement and any amendment thereto does not, when it becomes
effective, contain an untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading and (iii) each of the Prospectus forming a part of the
Shelf Registration Statement, and any



                                                                             -6-
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amendment or supplement to such Prospectus, does not at any time during the
Effectiveness Period include an untrue statement of a material fact or omit to
state a material fact necessary in order to make the statements therein, in the
light of the circumstances under which they were made, not misleading; provided,
however, that the Company shall not be required to prepare an amendment or
supplement to the Prospectus forming part of the Shelf Registration Statement
during any period from time to time during which the use of the Prospectus may
be suspended by the Company as permitted by this Agreement, after giving written
notice of such suspension to the Holders as required by this Agreement.

         (d)   The Company shall promptly advise each Electing Holder, and
shall confirm such advice in writing if so requested by any such Electing
Holder:

                  (i) when the Shelf Registration Statement and any amendment
         thereto has been filed with the Commission and when the Shelf
         Registration Statement or any post-effective amendment thereto has
         become effective, in each case making a public announcement thereof by
         release made to Reuters Economic Services and Bloomberg Business News;

                  (ii) of the receipt by the Company of any request by the
         Commission for amendments or supplements to the Shelf Registration
         Statement or the Prospectus included therein or for additional
         information in relation thereto;

                  (iii) of the issuance by the Commission of any stop order
         suspending the effectiveness of the Shelf Registration Statement or the
         initiation of any proceedings for such purpose;

                  (iv) of the receipt by the Company of any notification with
         respect to the suspension of the qualification of the securities
         included in the Shelf Registration Statement for sale in any
         jurisdiction or the initiation of any proceeding for such purpose; and

                  (v) of the happening of any event or the existence of any
         state of facts that requires the making of any changes in the Shelf
         Registration Statement or the Prospectus included therein so that, as
         of such date, such Shelf Registration Statement and Prospectus do not
         contain an untrue statement of a material fact and do not omit to state
         a material fact required to be stated therein or necessary to make the
         statements therein (in the case of the Prospectus, in light of the
         circumstances under which they were made) not misleading (which advice
         shall be accompanied by an instruction to such Electing Holders to
         suspend the use of the Prospectus until the requisite changes have been
         made; provided that the Company shall not be permitted to suspend the
         use of the Prospectus for more than an aggregate of 30 days in any
         90-day period or 90 days in any 12-month period unless the Company
         complies with its obligations to pay Liquidated Damages as set forth in
         Section 7 hereof).


                                                                             -7-
<PAGE>
         (e) The Company shall use all reasonable efforts to prevent the
issuance, and if issued, to obtain the withdrawal at the earliest reasonably
practicable time, of any order suspending the effectiveness of the Shelf
Registration Statement.

         (f) The Company shall furnish to each Electing Holder, without charge,
at least one copy of the Shelf Registration Statement and all post-effective
amendments thereto, including financial statements and schedules, and, if such
Electing Holder so requests in writing, all reports, other documents and
exhibits that are filed with or incorporated by reference in the Shelf
Registration Statement.

         (g) The Company shall, during the Effectiveness Period, deliver to each
Electing Holder, without charge, as many copies of the Prospectus (including
each preliminary Prospectus) included in the Shelf Registration Statement and
any amendment or supplement thereto as such Electing Holder may reasonably
request; and the Company consents (except during the periods specified in
Section 2(c) above or during the continuance of any event described in Section
3(d)(v) above) to the use of the Prospectus and any amendment or supplement
thereto by each of the Electing Holders in connection with the offering and sale
of the Registrable Securities covered by the Prospectus and any amendment or
supplement thereto during the Effectiveness Period.

         (h) Prior to any offering of Registrable Securities pursuant to the
Shelf Registration Statement, the Company shall (i) register or qualify or
cooperate with the Electing Holders and their respective counsel in connection
with the registration or qualification of such Registrable Securities for offer
and sale under the securities or "blue sky" laws of such jurisdictions within
the United States as any Electing Holder may reasonably request in writing, (ii)
keep such registrations or qualifications in effect and comply with such laws so
as to permit the continuance of offers and sales in such jurisdictions for so
long as may be necessary to enable any Electing Holder or underwriter, if any,
to complete its distribution of Registrable Securities pursuant to the Shelf
Registration Statement, and (iii) take any and all other actions necessary or
advisable to enable the disposition in such jurisdictions of such Registrable
Securities; provided, however, that in no event shall the Company be obligated
to (A) qualify as a foreign corporation or as a dealer in securities in any
jurisdiction where it would not otherwise be required to so qualify but for this
Section 3(h), (B) file any general consent to service of process in any
jurisdiction where it is not as of the date hereof so subject or (C) subject
itself to taxation in any jurisdiction if it is not so subject.

         (i) Unless any Registrable Securities shall be in book-entry only form,
the Company shall cooperate with the Electing Holders to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be sold pursuant to the Shelf Registration Statement, which certificates, if so
required by any securities exchange upon which any Registrable Securities are
listed, shall be penned, lithographed or engraved, or produced by any
combination of such methods, on steel engraved borders, and which certificates
shall be free of any restrictive legends and in such permitted denominations and
registered in such names as Electing Holders may request in connection with the
sale of Registrable Securities pursuant to the Shelf Registration Statement.


                                                                             -8-
<PAGE>
         (j) Upon the occurrence of any fact or event contemplated by Section
3(d)(v) above and subject to Section 3(c), the Company shall promptly prepare a
post-effective amendment to the Shelf Registration Statement or an amendment or
supplement to the related Prospectus or file any other required document so
that, as thereafter delivered to purchasers of the Registrable Securities
included therein, the Prospectus will not include an untrue statement of a
material fact or omit to state any material fact necessary to make the
statements therein, in the light of the circumstances under which they were
made, not misleading. If the Company notifies the Electing Holders of the
occurrence of any fact or event contemplated by Section 3(d)(v) above, the
Electing Holders shall suspend the use of the Prospectus until the requisite
changes to the Prospectus have been made.

         (k) Not later than the Effective Time of the Shelf Registration
Statement, the Company shall provide a CUSIP number for the Registrable
Securities that are debt securities.

         (l) The Company shall use its best efforts to comply with all
applicable Rules and Regulations, and use all reasonable efforts to make
generally available to its securityholders as soon as practicable, but in any
event not later than eighteen months after (i) the effective date (as defined in
Rule 158(c) under the Securities Act) of the Shelf Registration Statement, (ii)
the effective date of each post-effective amendment to the Shelf Registration
Statement, and (iii) the date of each filing by the Company with the Commission
of an Annual Report on Form 10-K that is incorporated by reference in the Shelf
Registration Statement, an earning statement of the Company and its subsidiaries
complying with Section 11(a) of the Securities Act and the rules and regulations
of the Commission thereunder (including, at the option of the Company, Rule
158).

         (m) Not later than the Effective Time of the Shelf Registration
Statement, the Company shall cause the Indenture to be qualified under the Trust
Indenture Act; in connection with such qualification, the Company shall
cooperate with the Trustee under the Indenture and the Holders (as defined in
the Indenture) to effect such changes to the Indenture as may be required for
such Indenture to be so qualified in accordance with the terms of the Trust
Indenture Act; and the Company shall execute, and shall use all reasonable
efforts to cause the Trustee to execute, all documents that may be required to
effect such changes and all other forms and documents required to be filed with
the Commission to enable such Indenture to be so qualified in a timely manner.
In the event that any such amendment or modification referred to in this Section
3(m) involves the appointment of a new trustee under the Indenture, the Company
shall appoint a new trustee thereunder pursuant to the applicable provisions of
the Indenture.

         (n) In the event of an underwritten offering conducted pursuant to
Section 6 hereof, the Company shall, if requested, promptly include or
incorporate in a Prospectus supplement or post-effective amendment to the Shelf
Registration Statement such information as the Managing Underwriters reasonably
agree should be included therein and to which the Company does not reasonably
object and shall make all required filings of such Prospectus supplement or
post-effective amendment as soon as reasonably practicable after it is notified
of the matters to be included or incorporated in such Prospectus supplement or
post-effective amendment.


                                                                             -9-
<PAGE>
         (o) The Company shall enter into such customary agreements (including
an underwriting agreement in customary form in the event of an underwritten
offering conducted pursuant to Section 6 hereof) and take all other appropriate
action in order to expedite and facilitate the registration and disposition of
the Registrable Securities, and in connection therewith, if an underwriting
agreement is entered into, cause the same to contain indemnification provisions
and procedures substantially identical to those set forth in Section 5 hereof
with respect to all parties to be indemnified pursuant to Section 5 hereof.

         (p)      The Company shall:

                  (i)(A) make reasonably available for inspection by the
         Electing Holders, any underwriter participating in any disposition
         pursuant to the Shelf Registration Statement, and any attorney,
         accountant or other agent retained by such Electing Holders or any such
         underwriter all relevant financial and other records, pertinent
         corporate documents and properties of the Company and its subsidiaries,
         and (B) cause the Company's officers, directors and employees to supply
         or make reasonably available for inspection all information reasonably
         requested by such Electing Holders or any such underwriter, attorney,
         accountant or agent in connection with the Shelf Registration
         Statement, in each case, as is customary for similar due diligence
         examinations; provided, however, that all records, information and
         documents that are designated in writing by the Company, in good faith,
         as confidential shall be kept confidential by such Electing Holders and
         any such underwriter, attorney, accountant or agent, unless such
         disclosure is made in connection with a court proceeding or required by
         law, or such records, information or documents become available to the
         public generally or through a third party without an accompanying
         obligation of confidentiality; and provided further that, if the
         foregoing inspection and information gathering would otherwise disrupt
         the Company's conduct of its business, such inspection and information
         gathering shall, to the greatest extent possible, be coordinated on
         behalf of the Electing Holders and the other parties entitled thereto
         by one counsel designated by and on behalf of the Electing Holders and
         other parties;

                  (ii) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, make such representations and warranties
         to the Electing Holders participating in such underwritten offering and
         to the Managing Underwriters, in form, substance and scope as are
         customarily made by the Company to underwriters in primary underwritten
         offerings of equity and convertible debt securities and covering
         matters including, but not limited to, those set forth in the Purchase
         Agreement;

                  (iii) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, obtain opinions of counsel to the Company
         (which counsel and opinions (in form, scope and substance) shall be
         reasonably satisfactory to the Managing Underwriters) addressed to each
         Electing Holder participating in such underwritten offering and the
         underwriters, covering such matters as are customarily covered in
         opinions requested in primary underwritten offerings of equity and
         convertible debt securities and such other matters as may be reasonably
         requested by such Electing Holders and underwriters (it being agreed
         that the matters to be covered by such


                                                                            -10-
<PAGE>
         opinions (or included therein as a written statement) shall include in
         customary form, without limitation, as of the date of the opinion and
         as of the Effective Time of the Shelf Registration Statement or most
         recent post-effective amendment thereto, as the case may be, the
         absence from the Shelf Registration Statement and the Prospectus,
         including the documents incorporated by reference therein, of an untrue
         statement of a material fact or the omission of a material fact
         required to be stated therein or necessary to make the statements
         therein not misleading;

                  (iv) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, obtain "cold comfort" letters and updates
         thereof from the independent public accountants of the Company (and, if
         necessary, from the independent public accountants of any subsidiary of
         the Company or of any business acquired by the Company for which
         financial statements and financial data are, or are required to be,
         included in the Shelf Registration Statement), addressed to each
         Electing Holder participating in such underwritten offering (if such
         Electing Holder has provided such letter, representations or
         documentation, if any, required for such cold comfort letter to be so
         addressed) and the underwriters, in customary form and covering matters
         of the type customarily covered in "cold comfort" letters in connection
         with primary underwritten offerings of equity and convertible debt
         securities;

                  (v) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, deliver such documents and certificates
         as may be reasonably requested by any Electing Holders participating in
         such underwritten offering and the Managing Underwriters, if any,
         including, without limitation, certificates to evidence compliance with
         Section 3(j) hereof and with any conditions contained in the
         underwriting agreement or other agreements entered into by the Company.

         (q) The Company will use all reasonable efforts to cause the Common
Stock issuable upon conversion of the Securities to be listed for quotation on
the Nasdaq National Market System or other stock exchange or trading system on
which the Common Stock primarily trades on or prior to the Effective Time of the
Shelf Registration Statement hereunder.

         (r) In the event that any broker-dealer registered under the Exchange
Act shall be an "affiliate" (as defined in Rule 2720(b)(1) of the NASD Rules (or
any successor provision thereto)) of the Company or has a "conflict of interest"
(as defined in Rule 2720(b)(7) of the NASD Rules (or any successor provision
thereto)) and such broker-dealer shall underwrite, participate as a member of an
underwriting syndicate or selling group or assist in the distribution of any
Registrable Securities covered by the Shelf Registration Statement, whether as a
Holder of such Registrable Securities or as an underwriter, a placement or sales
agent or a broker or dealer in respect thereof, or otherwise, the Company shall
assist such broker-dealer in complying with the requirements of the NASD Rules,
including, without limitation, by (A) engaging a "qualified independent
underwriter" (as defined in Rule 2720(b)(15) of the NASD Rules (or any successor
provision thereto)) to participate in the preparation of the registration
statement relating to such Registrable Securities, to exercise usual standards
of due diligence in respect thereto and to recommend the public offering price
of such Registrable Securities, (B) indemnifying such qualified independent
underwriter to the extent of the indemnification of


                                                                            -11-
<PAGE>
underwriters provided in Section 5 hereof, and (C) providing such information to
such broker-dealer as may be required in order for such broker-dealer to comply
with the requirements of the NASD Rules.

         (s) The Company shall use all reasonable efforts to take all other
steps necessary to effect the registration, offering and sale of the Registrable
Securities covered by the Shelf Registration Statement contemplated hereby.

         (t) The Company may require each Electing Holder with respect to the
Shelf Registration Statement to furnish to the Company such information
regarding the Electing Holder and the distribution of the Registrable Securities
held by such Electing Holder as may be required by applicable law or regulation
for inclusion in such Shelf Registration Statement, and the Company may exclude
from such registration the Registrable Securities of any Electing Holder that
fails to furnish such information within a reasonable time after receiving such
request.

         4. Registration Expenses. Except as otherwise provided in Section 3 or
6, the Company shall bear all fees and expenses incurred in connection with the
performance of its obligations under Sections 2, 3 and 6 hereof and shall bear
or reimburse the Electing Holders for the reasonable fees and disbursements of a
single counsel selected by a plurality of all Electing Holders who own an
aggregate of not less than 25% of the Registrable Securities covered by the
Shelf Registration Statement to act as counsel for all of the Electing Holders
in connection therewith. Each Electing Holder shall pay all underwriting
discounts and commissions and transfer taxes, if any, relating to the sale or
disposition of such Electing Holder's Registrable Securities pursuant to the
Shelf Registration Statement.

         5. Indemnification and Contribution.

         (a) Indemnification by the Company. Upon the registration of the
Registrable Securities pursuant to Section 2 hereof, the Company shall indemnify
and hold harmless each Electing Holder and each underwriter, selling agent or
other securities professional, if any, which facilitates the disposition of
Registrable Securities, and each of their respective officers and directors and
each person who controls such Electing Holder, underwriter, selling agent or
other securities professional within the meaning of Section 15 of the Securities
Act or Section 20 of the Exchange Act (each such person being sometimes referred
to as an "Indemnified Person") against any losses, claims, damages or
liabilities, joint or several, to which such Indemnified Person may become
subject under the Securities Act or otherwise, insofar as such losses, claims,
damages or liabilities (or actions in respect thereof) arise out of or are based
upon an untrue statement or alleged untrue statement of a material fact
contained in the Shelf Registration Statement under which such Registrable
Securities are to be registered under the Securities Act, or any Prospectus
contained therein or furnished by the Company to any Indemnified Person, or any
amendment or supplement thereto, or arise out of or are based upon the omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein (in the case of any
Prospectus or any amendment or supplement thereto, in the light of the
circumstances under which they were made) not misleading, and the Company hereby
agrees to reimburse such Indemnified Person


                                                                            -12-
<PAGE>
for any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such action or claim as such expenses are
incurred; provided, however, that the Company shall not be liable to any such
Indemnified Person in any such case to the extent that any such loss, claim,
damage, liability or expense arises out of or is based upon an untrue statement
or alleged untrue statement or omission or alleged omission made in such Shelf
Registration Statement or Prospectus, or amendment or supplement, in reliance
upon and in conformity with written information furnished to the Company by or
on behalf of such Indemnified Person expressly for use therein; provided,
further, in a disposition of Registrable Securities that does not involve (in
whole or in part) an underwritten offering conducted pursuant to Section 6
hereof, the Company shall not be liable to any Electing Holder or any officer
and director and each person who controls such Electing Holder (an "Indemnified
Electing Holder") pursuant to the foregoing to the extent that any such loss,
claim, damage, liability or expense of such Indemnified Electing Holder results
from the fact that such Indemnified Electing Holder sold Registrable Securities
to a person as to whom it shall be established by conclusive evidence that there
was not sent or given, at or prior to the written confirmation of such a sale, a
copy of the Prospectus (excluding documents incorporated by reference) or the
Prospectus as then amended or supplemented (excluding documents incorporated by
reference) in any case where such delivery is required by the Act, if the
Company has previously furnished copies thereof upon request therefor in
sufficient quantity to such Indemnified Electing Holder and the loss, claim,
damage, liability or expense of such Indemnified Electing Holder results from an
untrue statement or omission of a material fact contained in the preliminary
prospectus which was identified in writing at such time to such Indemnified
Electing Holder and corrected in the Prospectus (excluding any document
incorporated by reference) or in the Prospectus as then amended or supplemented
(excluding documents incorporated by reference) and such correction would have
cured the defect giving rise to such loss, claim, damage, liability or expense.

         (b) Indemnification by the Electing Holders and any Agents and
Underwriters. Each Electing Holder agrees, as a consequence of the inclusion of
any of such Electing Holder's Registrable Securities in such Shelf Registration
Statement, and each underwriter, selling agent or other securities professional,
if any, which facilitates the disposition of Registrable Securities shall agree,
as a consequence of facilitating such disposition of Registrable Securities,
severally and not jointly, to (i) indemnify and hold harmless the Company, its
directors, officers who sign any Shelf Registration Statement and each person,
if any, who controls the Company within the meaning of either Section 15 of the
Securities Act or Section 20 of the Exchange Act, against any losses, claims,
damages or liabilities to which the Company or such other persons may become
subject, under the Securities Act or otherwise, insofar as such losses, claims,
damages or liabilities (or actions in respect thereof) arise out of or are based
upon an untrue statement or alleged untrue statement of a material fact
contained in such Shelf Registration Statement or Prospectus, or any amendment
or supplement, or arise out of or are based upon the omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein (in the case of the Prospectus or any
amendment or supplement thereto, in the light of the circumstances under which
they were made) not misleading, in each case to the extent, but only to the
extent, that such untrue statement or alleged untrue statement or omission or
alleged omission was made in reliance upon and in


                                                                            -13-
<PAGE>
conformity with written information furnished to the Company by or on behalf of
such Electing Holder, underwriter, selling agent or other securities
professional expressly for use therein, and (ii) reimburse the Company and such
other persons for any legal or other expenses reasonably incurred by the Company
and/or such other persons in connection with investigating or defending any such
action or claim as such expenses are incurred.

         (c) Notices of Claims, Etc. Promptly after receipt by an indemnified
party under subsection (a) or (b) above of notice of the commencement of any
action, such indemnified party shall, if a claim in respect thereof is to be
made against an indemnifying party under this Section 5, notify such
indemnifying party in writing of the commencement thereof; but the omission so
to notify the indemnifying party shall not relieve it from any liability which
it may have to any indemnified party otherwise than under the indemnification
provisions of subsection (a) or (b) above. In case any such action shall be
brought against any indemnified party and it shall notify an indemnifying party
of the commencement thereof, such indemnifying party shall be entitled to
participate therein and, to the extent that it shall wish, jointly with any
other indemnifying party similarly notified, to assume the defense thereof, with
counsel reasonably satisfactory to such indemnified party (who shall not, except
with the consent of the indemnified party, be counsel to the indemnifying
party), and, after notice from the indemnifying party to such indemnified party
of its election so to assume the defense thereof, such indemnifying party shall
not be liable to such indemnified party under this Section 5 for any legal
expenses of other counsel or any other expenses, in each case subsequently
incurred by such indemnified party, in connection with the defense thereof,
other than reasonable costs of investigation. No indemnifying party shall,
without the written consent of the indemnified party, effect the settlement or
compromise of, or consent to the entry of any judgment with respect to, any
pending or threatened action or claim in respect of which indemnification or
contribution may be sought hereunder (whether or not the indemnified party is an
actual or potential party to such action or claim) unless such settlement,
compromise or judgment (i) includes an unconditional release of the indemnified
party from all liability arising out of such action or claim and (ii) does not
include a statement as to, or an admission of, fault, culpability or a failure
to act, by or on behalf of any indemnified party. In no event shall the
indemnifying party or parties be liable for the fees and expenses of more than
one counsel (in addition to any local counsel) separate from its own counsel for
all indemnified parties in connection with any one action or separate but
related actions in the same jurisdiction arising out of the same general
allegations or circumstances.

         (d) Contribution. If the indemnification provided for in this Section 5
is unavailable to or insufficient to hold harmless an indemnified party under
subsection (a) or (b) above in respect of any losses, claims, damages or
liabilities (or actions in respect thereof) referred to therein, then each
indemnifying party shall contribute to the amount paid or payable by such
indemnified party as a result of such losses, claims, damages or liabilities (or
actions in respect thereof) in such proportion as is appropriate to reflect the
relative fault of the indemnifying party and the indemnified party in connection
with the statements or omissions which resulted in such losses, claims, damages
or liabilities (or actions in respect thereof), as well as any other relevant
equitable considerations. The relative fault of such indemnifying party and
indemnified party shall be determined by reference to, among other things,
whether the untrue or alleged


                                                                            -14-
<PAGE>
untrue statement of a material fact or omission or alleged omission to state a
material fact relates to information supplied by such indemnifying party or by
such indemnified party, and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.
The parties hereto agree that it would not be just and equitable if contribution
pursuant to this Section 5(d) were determined by pro rata allocation (even if
the Electing Holders or any underwriters, selling agents or other securities
professionals or all of them were treated as one entity for such purpose) or by
any other method of allocation which does not take account of the equitable
considerations referred to in this Section 5(d). The amount paid or payable by
an indemnified party as a result of the losses, claims, damages or liabilities
(or actions in respect thereof) referred to above shall be deemed to include any
legal or other fees or expenses reasonably incurred by such indemnified party in
connection with investigating or defending any such action or claim. No person
guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of
the Securities Act) shall be entitled to contribution from any person who was
not guilty of such fraudulent misrepresentation. The obligations of the Electing
Holders and any underwriters, selling agents or other securities professionals
in this Section 5(d) to contribute shall be several in proportion to the
percentage of principal amount of Registrable Securities registered or
underwritten, as the case may be, by them and not joint.

         (e) Notwithstanding any other provision of this Section 5, in no event
will any (i) Electing Holder be required to undertake liability to any person
under this Section 5 for any amounts in excess of the dollar amount of the
proceeds to be received by such Holder from the sale of such Holder's
Registrable Securities (after deducting any fees, discounts and commissions
applicable thereto) pursuant to the Shelf Registration Statement under which
such Registrable Securities are to be registered under the Securities Act and
(ii) underwriter, selling agent or other securities professional be required to
undertake liability to any person hereunder for any amounts in excess of the
discount, commission or other compensation payable to such underwriter, selling
agent or other securities professional with respect to the Registrable
Securities underwritten by it and distributed to the public.

         (f) The obligations of the Company under this Section 5 shall be in
addition to any liability which the Company may otherwise have to any
Indemnified Person and the obligations of any Indemnified Person under this
Section 5 shall be in addition to any liability which such Indemnified Person
may otherwise have to the Company or the other persons to be indemnified under
Section 5(b) hereof. The remedies provided in this Section 5 are not exclusive
and shall not limit any rights or remedies which may otherwise be available to
an indemnified party at law or in equity.

         6. Underwritten Offering. Any Holder of Registrable Securities who
desires to do so may sell Registrable Securities (in whole or in part) in an
underwritten offering; provided that (i) the Electing Holders of at least
33-1/3% in aggregate principal amount of the Registrable Securities then covered
by the Shelf Registration Statement shall request such an offering and (ii) at
least such aggregate principal amount of such Registrable Securities shall be
included in such offering; and provided further that the Company shall not be
obligated to cooperate with more than one underwritten offering during the
Effectiveness Period. Upon receipt of such a request, the Company shall provide
all Holders of Registrable Securities prompt written notice


                                                                            -15-
<PAGE>
of the request, which notice shall inform such Holders that they have the
opportunity to participate in the offering. In any such underwritten offering,
the investment banker or bankers and manager or managers that will administer
the offering will be selected by, and the underwriting arrangements with respect
thereto (including the size of the offering) will be approved by, the Holders of
a majority of the Registrable Securities to be included in such offering;
provided, however, that such investment bankers and managers and underwriting
arrangements must be reasonably satisfactory to the Company. No Holder may
participate in any underwritten offering contemplated hereby unless (a) such
Holder agrees to sell such Holder's Registrable Securities to be included in the
underwritten offering in accordance with any approved underwriting arrangements,
(b) such Holder completes and executes all reasonable questionnaires, powers of
attorney, indemnities, underwriting agreements, lock-up letters and other
documents required under the terms of such approved underwriting arrangements,
and (c) if such Holder is not then an Electing Holder, such Holder returns a
completed and signed Notice and Questionnaire to the Company in accordance with
Section 3(a)(ii) hereof within a reasonable amount of time before such
underwritten offering. The Holders participating in any underwritten offering
shall be responsible for any underwriting discounts and commissions and fees
and, subject to Section 4 hereof, expenses of their own counsel. The Company
shall pay all expenses customarily borne by issuers in an underwritten offering,
including but not limited to filing fees, the fees and disbursements of its
counsel and independent public accountants and any printing expenses incurred in
connection with such underwritten offering. Notwithstanding the foregoing or the
provisions of Section 3(n) hereof, upon receipt of a request from the Managing
Underwriter or a representative of Holders of a majority of the Registrable
Securities to be included in an underwritten offering to prepare and file an
amendment or supplement to the Shelf Registration Statement and Prospectus in
connection with an underwritten offering, the Company may delay the filing of
any such amendment or supplement for up to 90 days if the Board of Directors of
the Company shall have determined in good faith that the Company has a bona fide
business reason for such delay.

         7. Liquidated Damages.

         (a) Pursuant to Section 2(a) hereof, the Company may, upon written
notice to all the Holders, postpone having the Shelf Registration Statement
filed or declared effective for a reasonable period not to exceed 90 days if the
Company possesses material non-public information, the disclosure of which would
have a material adverse effect on the Company and its subsidiaries taken as a
whole. Notwithstanding any such postponement, if (i) on or prior to the 90th day
following the Closing Date, a Shelf Registration Statement has not been filed
with the Commission or (ii) on or prior to the 180th day following the Closing
Date, such Shelf Registration Statement is not declared effective by the
Commission (each, a "Registration Default"), the Company shall be required to
pay liquidated damages ("Liquidated Damages"), from and including the day
following such Registration Default until such Shelf Registration Statement is
either so filed or so filed and subsequently declared effective, as applicable,
or, if earlier, the end of the Effectiveness Period, at a rate per annum equal
to an additional one-quarter of one percent (0.25%) of the principal amount of
Registrable Securities, to and including the 90th day following such
Registration Default and one-half of one percent (0.5%) thereof from and after
the 91st day following such Registration Default.


                                                                            -16-
<PAGE>
         (b) In the event that the Shelf Registration Statement ceases to be
effective (or the Holders of Registrable Securities are otherwise prevented or
restricted by the Company from effecting sales pursuant thereto) (an "Effective
Failure") during the Effective Period for more than 30 days, whether or not
consecutive, in any 90-day period, or for more than 90 days, whether or not
consecutive, during any 12-month period, then the Company shall pay Liquidated
Damages at a rate per annum equal to an additional one-half of one percent
(0.5%) of the principal amount of Registrable Securities from the 31st day of
the applicable 90-day period or the 91st day of the applicable 12-month period,
as the case may be, that such Shelf Registration Statement ceases to be
effective (or the Holders of Registrable Securities are otherwise prevented or
restricted by the Company from effecting sales pursuant thereto) until the
earlier of (i) the time the Shelf Registration Statement again becomes effective
or the Holders of Registrable Securities are again able to make sales under the
Shelf Registration Statement or (ii) the time the Effectiveness Period expires.
For the purpose of determining an Effective Failure, days on which the Company
has been obligated to pay Liquidated Damages in accordance with the foregoing in
respect of a prior Effective Failure within the applicable 90-day or 12-month
period, as the case may be, shall not be included.

         (c) Any amounts to be paid as Liquidated Damages pursuant to paragraphs
(a) or (b) of this Section 7 shall be paid semi-annually in arrears, with the
first semi-annual payment due on the first Interest Payment Date (as defined in
the Indenture), as applicable, following the date of such Registration Default.
Such Liquidated Damages will accrue (1) in respect of the Securities at the
rates set forth in paragraphs (a) or (b) of this Section 7, as applicable, on
the principal amount of the Securities and (2) in respect of the Common Stock
issued upon conversion of the Securities, at the rates set forth in paragraphs
(a) or (b) of this Section 7, as applicable, applied to the Conversion Price (as
defined in the Indenture) at that time.

         (e) Except as provided in Section 8(b) hereof, the Liquidated Damages
as set forth in this Section 7 shall be the exclusive monetary remedy available
to the Holders of Registrable Securities for such Registration Default or
Effective Failure. In no event shall the Company be required to pay Liquidated
Damages in excess of the applicable maximum amount of one-half of one percent
(0.5%) set forth above, regardless of whether one or multiple Registration
Defaults and/or Effective Failures exist.

         8. Miscellaneous.

         (a) Other Registration Rights. The Company may have granted and may in
the future grant registration rights that would permit any person that is a
third party the right to piggy-back on any Shelf Registration Statement,
provided that if the Managing Underwriter of any underwritten offering conducted
pursuant to Section 6 hereof notifies the Company and the Electing Holders that
the total amount of securities which the Electing Holders and the holders of
such piggy-back rights intend to include in any Shelf Registration Statement is
so large as to materially threaten the success of such offering (including the
price at which such securities can be sold), then the amount, number or kind of
securities to be offered for the account of holders of such piggy-back rights
will be reduced to the extent necessary to reduce the total amount of securities
to be included in such offering to the amount, number and kind recommended by
the


                                                                            -17-
<PAGE>
Managing Underwriter prior to any reduction in the amount of Registrable
Securities to be included in such Shelf Registration Statement.

         (b) Specific Performance. The parties hereto acknowledge that there
would be no adequate remedy at law if the Company fails to perform any of its
obligations hereunder and that the Purchasers and the Holders from time to time
may be irreparably harmed by any such failure, and accordingly agree that the
Purchasers and such Holders, in addition to any other remedy to which they may
be entitled at law or in equity and without limiting the remedies available to
the Electing Holders under Section 7 hereof, shall be entitled to compel
specific performance of the obligations of the Company under this Agreement in
accordance with the terms and conditions of this Agreement, in any court of the
United States or any State thereof having jurisdiction.

         (c) Amendments and Waivers. This Agreement, including this Section
8(c), may be amended, and waivers or consents to departures from the provisions
hereof may be given, only by a written instrument duly executed by the Company
and the Holders of a majority in aggregate principal amount of Registrable
Securities then outstanding. Each Holder of Registrable Securities outstanding
at the time of any such amendment, waiver or consent or thereafter shall be
bound by any amendment, waiver or consent effected pursuant to this Section
8(c), whether or not any notice, writing or marking indicating such amendment,
waiver or consent appears on the Registrable Securities or is delivered to such
Holder.

         (d) Notices. All notices and other communications provided for or
permitted hereunder shall be given as provided in the Indenture.

         (e) Parties in Interest. The parties to this Agreement intend that all
Holders of Registrable Securities shall be entitled to receive the benefits of
this Agreement and that any Electing Holder shall be bound by the terms and
provisions of this Agreement by reason of such election with respect to the
Registrable Securities which are included in the Shelf Registration Statement.
All of the terms and provisions of this Agreement shall be binding upon, shall
inure to the benefit of and shall be enforceable by the respective successors
and assigns of the parties hereto and any Holder from time to time of the
Registrable Securities to the aforesaid extent. In the event that any transferee
of any Holder of Registrable Securities shall acquire Registrable Securities, in
any manner, whether by gift, bequest, purchase, operation of law or otherwise,
such transferee shall, without any further writing or action of any kind, be
entitled to receive the benefits of and, if an Electing Holder, be conclusively
deemed to have agreed to be bound by and to perform all of the terms and
provisions of this Agreement to the aforesaid extent.

         (f) Counterparts. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

         (g) Headings. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.


                                                                            -18-
<PAGE>
         (h) GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING EFFECT TO ANY
PROVISIONS RELATING TO CONFLICTS OF LAWS.

         (i) Severability. In the event that any one or more of the provisions
contained herein, or the application thereof in any circumstances, is held
invalid, illegal or unenforceable in any respect for any reason, the validity,
legality and enforceability of any such provision in every other respect and of
the remaining provisions hereof shall not be in any way impaired or affected
thereby, it being intended that all of the rights and privileges of the parties
hereto shall be enforceable to the fullest extent permitted by law.

         (j) Survival. The respective indemnities, agreements, representations,
warranties and other provisions set forth in this Agreement or made pursuant
hereto shall remain in full force and effect, regardless of any investigation
(or any statement as to the results thereof) made by or on behalf of any
Electing Holder, any director, officer or partner of such Holder, any agent or
underwriter, any director, officer or partner of such agent or underwriter, the
Company, any director, officer or employee of the Company, or any controlling
person of any of the foregoing, and shall survive the transfer and registration
of the Registrable Securities of such Holder.


                                                                            -19-
<PAGE>
         Please confirm that the foregoing correctly sets forth the agreement
between the Company and you.

                                     Very truly yours,

                                     ATMI, Inc.


                                     By:
                                        ----------------------------------------
                                            Name:
                                            Title:

Accepted as of the date hereof:
Goldman, Sachs & Co.
Merrill Lynch Pierce Fenner & Smith Incorporated


By:
   -----------------------------------------------
              Authorized Signatory


                                       20
<PAGE>
                                                                      APPENDIX A



                                   ATMI, INC.


                         INSTRUCTION TO DTC PARTICIPANTS

                                (Date of Mailing)

                     URGENT - IMMEDIATE ATTENTION REQUESTED

                          DEADLINE FOR RESPONSE: [DATE]


                  The Depository Trust Company ("DTC") has identified you as a
DTC Participant through which beneficial interests in the ATMI, Inc. (the
"Company") 5.25% Convertible Subordinated Notes due November 15, 2006 (the
"Notes") are held.

                  The Company is in the process of registering the Notes and the
shares of common stock, par value $0.01 per share, issuable upon conversion
thereof (together, the "Securities") under the Securities Act of 1933, as
amended, for resale by the beneficial owners thereof. In order to have their
Securities included in the registration statement, beneficial owners, including
beneficial owners resident outside the United States, must complete and return
the enclosed Notice of Registration Statement and Selling Securityholder
Questionnaire (the "Notice and Questionnaire").

                  It is important that beneficial owners of the Securities
receive a copy of the enclosed materials as soon as possible as their rights to
have the Securities included in the registration statement depend upon their
returning the Notice and Questionnaire by [DEADLINE FOR RESPONSE]. Please
forward a copy of the enclosed documents to each beneficial owner that holds
interests in the Securities through you. If you require more copies of the
enclosed materials or have any questions pertaining to this matter, please
contact [NAME, ADDRESS AND TELEPHONE NUMBER OF CONTACT AT THE ISSUER].


                                                                            -21-
<PAGE>
                                   ATMI, INC.


                        Notice of Registration Statement
                                       and
                      Selling Securityholder Questionnaire


                                     [DATE]


                  ATMI, Inc. (the "Company") has filed or intends shortly to
file with the United States Securities and Exchange Commission (the
"Commission") a registration statement on Form S-3 (the "Shelf Registration
Statement") for the registration and resale under Rule 415 of the United States
Securities Act of 1933, as amended (the "Securities Act"), of the Company's
5.25% Convertible Subordinated Notes due November 15, 2006 (the "Securities")
and the shares of common stock, par value $0.01 per share (the "Common Stock"),
issuable upon conversion thereof, in accordance with the Registration Rights
Agreement, dated as of November 13, 2001 (the "Registration Rights Agreement"),
between the Company and the purchasers named therein. A copy of the Registration
Rights Agreement is attached hereto. All capitalized terms not otherwise defined
herein shall have the meanings ascribed thereto in the Registration Rights
Agreement.

                  In order to have Registrable Securities included in the Shelf
Registration Statement (or a supplement or amendment thereto), this Notice of
Registration Statement and Selling Securityholder Questionnaire ("Notice and
Questionnaire") must be completed, executed and delivered to the Company at the
address set forth herein for receipt ON OR BEFORE [DEADLINE FOR RESPONSE].
Beneficial owners of Registrable Securities who do not complete, execute and
return this Notice and Questionnaire by such date (i) will not be named as
selling securityholders in the Shelf Registration Statement and (ii) may not use
the Prospectus forming a part thereof for resales of Registrable Securities.
Beneficial owners of Registrable Securities who have not returned a Notice and
Questionnaire by the deadline set forth above may, however, receive another
Notice and Questionnaire from the Company upon request. Following its receipt of
a completed and signed Notice and Questionnaire, the Company will include the
Registrable Securities covered thereby in the Shelf Registration Statement
subject to restrictions on the timing and number of amendments to the Shelf
Registration Statement and other terms and conditions provided in the
Registration Rights Agreement.

                  Certain legal consequences arise from being named as a selling
securityholder in the Shelf Registration Statement and related Prospectus.
Accordingly, holders and beneficial owners of Registrable Securities are advised
to consult their own securities law counsel regarding the consequences of being
named or not being named as a selling securityholder in the Shelf Registration
Statement and related Prospectus.


                                                                            -22-
<PAGE>
                  The term "Registrable Securities" is defined in the
Registration Rights Agreement to mean all or any portion of the Securities
issued from time to time under the Indenture in registered form and the shares
of Common Stock issuable upon conversion or repurchase of such Securities;
provided, however, that a security ceases to be a Registrable Security when it
is no longer a Restricted Security.

                  The term "Restricted Security" is defined in the Registration
Rights Agreement to mean any Security or share of Common Stock issuable upon
conversion or repurchase thereof except any such Security or share of Common
Stock that (i) has been effectively registered under the Securities Act and sold
in a manner contemplated by the Shelf Registration Statement, (ii) has been
transferred in compliance with Rule 144 under the Securities Act (or any
successor provision thereto) or is transferable pursuant to paragraph (k) of
such Rule 144 (or any successor provision thereto), or (iii) has otherwise been
transferred and a new Security or share of Common Stock not subject to transfer
restrictions under the Securities Act has been delivered by or on behalf of the
Company in accordance with Section 3.5 of the Indenture.

                                    ELECTION

                  The undersigned holder (the "Selling Securityholder") of
Registrable Securities hereby elects to include in the Shelf Registration
Statement the Registrable Securities beneficially owned by it and listed below
in Item (3). The undersigned, by signing and returning this Notice and
Questionnaire, agrees to be bound with respect to such Registrable Securities by
the terms and conditions of this Notice and Questionnaire and the Registration
Rights Agreement, including, without limitation, Section 5 of the Registration
Rights Agreement, as if the undersigned Selling Securityholder were an original
party thereto.

                  Upon any sale of Registrable Securities pursuant to the Shelf
Registration Statement, the Selling Securityholder will be required to deliver
to the Company and the Trustee the Notice of Transfer (completed and signed) set
forth in Exhibit 1 to this Notice and Questionnaire.

                  The Selling Securityholder hereby provides the following
information to the Company and represents and warrants that such information is
accurate and complete:


                                                                            -23-
<PAGE>
                                  QUESTIONNAIRE


(1)  (a) Full Legal Name of Selling Securityholder:

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

     (b) Full Legal Name of Registered Holder (if not the same as in (a) above)
         of Registrable Securities Listed in Item (3) Below:

         -----------------------------------------------------------------------
     (c) Full Legal Name of DTC Participant (if applicable and if not the
         same as (b) above) Through Which Registrable Securities Listed in
         Item (3) Below are Held:

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

(2)        Address for Notices to Selling Securityholder:

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

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

                                ---------------------------------------
           Telephone:
                                ---------------------------------------
           Fax:
                                ---------------------------------------
           Contact Person:
                                ---------------------------------------


(3)       Beneficial Ownership of Securities:

          Except as set forth below in this Item (3), the undersigned Selling
          Securityholder does not beneficially own any Securities or shares of
          Common Stock issued upon conversion or repurchase of any Securities.

     (a)  Principal amount of Registrable Securities (as defined in the
          Registration Rights Agreement) beneficially owned:

          ---------------------------------------------------------------------
          CUSIP No(s). of such Registrable Securities:

          ---------------------------------------------------------------------
          Number of shares of Common Stock (if any) beneficially owned and
          issued to date upon conversion or repurchase of Registrable
          Securities:
                     -----------------------------------------------------------

     (b)  Principal amount of Securities other than Registrable Securities
          beneficially owned:
                             ---------------------------------------------------
          CUSIP No(s). of such other Securities:
                                                --------------------------------

          Number of shares of Common Stock (if any) beneficially owned and
          issued to date upon conversion or repurchase of such other
          Securities:
                     -----------------------------------------------------------

     (c)  Principal amount of Registrable Securities which the undersigned
          wishes to be included in the Shelf Registration Statement:

          ---------------------------------------------------------------------
          CUSIP No(s). of such Registrable Securities to be included in the
          Shelf Registration Statement:
                                       -----------------------------------------


                                                                            -24-
<PAGE>
          Number of shares of Common Stock (if any) beneficially owned and
          issued to date upon conversion or repurchase of Registrable
          Securities which are to be included in the Shelf Registration
          Statement:
                    ------------------------------------------------------------
(4)       Beneficial Ownership of Other Securities of the Company:

          Except as set forth below in this Item (4), the undersigned Selling
          Securityholder is not the beneficial or registered owner of any
          shares of Common Stock or any other securities of the Company, other
          than the Securities and shares of Common Stock listed above in Item
          (3).

          State any exceptions here:



(5)       Relationships with the Company:

          Except as set forth below, neither the Selling Securityholder nor any
          of its affiliates, officers, directors or principal equity holders
          (5% or more) has held any position or office or has had any other
          material relationship with the Company (or its predecessors or
          affiliates) during the past three years.

          State any exceptions here:



(6)       Plan of Distribution:

          Except as set forth below, the undersigned Selling Securityholder
          intends to distribute the Registrable Securities listed above in
          Item (3) only as follows (if at all): Such Registrable Securities
          may be sold from time to time directly by the undersigned Selling
          Securityholder or, alternatively, through underwriters,
          broker-dealers or agents. Such Registrable Securities may be sold in
          one or more transactions at fixed prices, at prevailing market
          prices at the time of sale, at varying prices determined at the time
          of sale, or at negotiated prices. Such sales may be effected in
          transactions (which may involve crosses or block transactions) (i)
          on any national securities exchange or quotation service on which
          the Registrable Securities may be listed or quoted at the time of
          sale, (ii) in the over-the-counter market, (iii) in transactions
          otherwise than on such exchanges or services or in the
          over-the-counter market, or (iv) through the writing of options. In
          connection with sales of the Registrable Securities or otherwise,
          the Selling Securityholder may enter into hedging transactions with
          broker-dealers, which may in turn engage in short sales of the
          Registrable Securities in the course of hedging the positions they
          assume. The Selling Securityholder may also sell Registrable
          Securities short and deliver Registrable Securities to close out
          such short positions, or loan or pledge Registrable Securities to
          broker-dealers that in turn may sell such securities.

          State any exceptions here:





                                                                            -25-
<PAGE>
         Note: In no event may such method(s) of distribution take the form of
an underwritten offering of the Registrable Securities without the prior
agreement of the Company.

         By signing below, the Selling Securityholder acknowledges that it
understands its obligation to comply, and agrees that it will comply, with the
prospectus delivery and other provisions of the Securities Act and the Exchange
Act and the rules and regulations thereunder, particularly Regulation M.

         In the event that the Selling Securityholder transfers all or any
portion of the Registrable Securities listed in Item (3) above after the date on
which such information is provided to the Company, the Selling Securityholder
agrees to notify the transferee(s) at the time of the transfer of its rights and
obligations under this Notice and Questionnaire and the Registration Rights
Agreement.

         By signing below, the Selling Securityholder consents to the disclosure
of the information contained herein in its answers to Items (1) through (6)
above and the inclusion of such information in the Shelf Registration Statement
and related Prospectus. The Selling Securityholder understands that such
information will be relied upon by the Company in connection with the
preparation of the Shelf Registration Statement and related Prospectus.

         In accordance with the Selling Securityholder's obligation, under
Section 3(a) of the Registration Rights Agreement, to provide such information
as may be required by law for inclusion in the Shelf Registration Statement, the
Selling Securityholder agrees to promptly notify the Company of any inaccuracies
or changes in the information provided herein which may occur subsequent to the
date hereof at any time while the Shelf Registration Statement remains in
effect. Each Holder further agrees to notify the Company within 10 business days
of request, of the amount of Registrable Securities sold pursuant to the Shelf
Registration Statement and, in the absence of a response, the Company may assume
that all of the Holder's Registrable Securities were so sold. All notices
hereunder and pursuant to the Registration Rights Agreement shall be made in
writing, by hand-delivery, first-class mail postage prepaid, or air courier
guaranteeing overnight delivery as follows:

         (i) To the Company:

                                  ATMI, Inc.
                                  7 Commerce Drive
                                  Danbury, CT 06810
                                  Attention:  Chief Financial Officer



         (ii) With a copy to:

                                  Kramer Levin Naftalis & Frankel LLP
                                  919 Third Avenue
                                  New York, New York  10022
                                  Attn:  Howard T. Spilko



                                                                            -26-
<PAGE>
         Once this Notice and Questionnaire is executed by the Selling
Securityholder and received by the Company, the terms of this Notice and
Questionnaire, and the representations and warranties contained herein, shall be
binding on, shall inure to the benefit of and shall be enforceable by the
respective successors, heirs, personal representatives, and assigns of the
Company and the Selling Securityholder (with respect to the Registrable
Securities beneficially owned by such Selling Securityholder and listed in Item
(3) above). This Agreement shall be governed in all respects by the laws of the
State of New York, without giving effect to any provisions related to conflicts
of laws.


                                                                            -27-
<PAGE>
         IN WITNESS WHEREOF, the undersigned, by authority duly given, has
caused this Notice and Questionnaire to be executed and delivered either in
person or by its duly authorized agent.

Dated:
        ----------------------------




      --------------------------------------------------------------------------
      Selling Securityholder
      (Print/type full legal name of beneficial owner of Registrable Securities)



      By:
        ------------------------------------------------------------------------
      Name:
      Title:



PLEASE RETURN THE COMPLETED AND EXECUTED NOTICE AND QUESTIONNAIRE FOR RECEIPT ON
OR BEFORE [DEADLINE FOR RESPONSE] TO THE COMPANY AT:

                       ATMI, Inc.
                       7 Commerce Drive
                       Danbury, CT 06810
                       Attention:  Chief Financial Officer





                                                                            -28-
<PAGE>
                                                                       EXHIBIT 1
                                                                   TO APPENDIX A


              NOTICE OF TRANSFER PURSUANT TO REGISTRATION STATEMENT

ATMI, Inc.
7 Commerce Drive
Danbury, CT 06810
Attention:  Chief Financial Officer

State Street Bank and Trust Company
Corporate Trust Department - LCC6
2 Avenue de Lafayette, 6th Floor
Boston, MA  02111
Attention:  Corporate Trust Department

                  Re:  ATMI, Inc. (the "Company")
                       5.25% Convertible Subordinated Notes due November 15,
                       2006 (the "Notes")

Dear Sirs:

                  Please be advised that _____________________ has transferred
$___________ aggregate principal amount of the above-referenced Notes or shares
of the Company's common stock, issued upon conversion or repurchase of Notes,
pursuant to an effective Registration Statement on Form S-3 (File No. 333-____)
filed by the Company.

                  We hereby certify that the prospectus delivery requirements,
if any, of the Securities Act of 1933, as amended, have been satisfied with
respect to the transfer described above and that the above-named beneficial
owner of the Notes or common stock is named as a selling securityholder in the
Prospectus dated [DATE], or in amendments or supplements thereto, and that the
aggregate principal amount of the Notes or number of shares of common stock
transferred are [A PORTION OF] the Notes or shares of common stock listed in
such Prospectus as amended or supplemented opposite such owner's name.

Dated:

                                                    Very truly yours,

                                                    ------------------------
                                                    (Name)

                                  By:               ------------------------
                                                    (Authorized Signature)



                                                                            -29-