<PAGE>

  As filed with the Securities and Exchange Commission on September 20, 2000

                                                     Registration No. 333-

================================================================================

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

                                   FORM S-8
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
                                ______________

                                  ATMI, INC.
            (Exact name of registrant as specified in its charter)

                     Delaware                                 06-1481060
           (State or other jurisdiction of                 (I.R.S. Employer
            incorporation or organization)                Identification No.)
                                ______________

          7 Commerce Drive, Danbury, Connecticut                  06810
         (Address of Principal Executive Offices)              (Zip Code)
                                ______________

                                  ATMI, Inc.
                                2000 Stock Plan
                           (Full title of the plan)
                                ______________

                               Eugene G. Banucci
                            Chief Executive Officer
                                  ATMI, Inc.
                               7 Commerce Drive
                          Danbury, Connecticut 06810
                    (Name and address of agent for service)
                                ______________

                                (203) 794-1100
         (Telephone number, including area code, of agent for service)
                                ______________

                                   Copy to:

                             Donna L. Brooks, Esq.
                             Shipman & Goodwin LLP
                               One American Row
                          Hartford, Connecticut 06103
                                (860) 251-5000

                       CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
=========================================================================================================================
                                                                                   Proposed
                                                           Proposed                maximum
    Title of Securities          Amount to be          maximum offering       aggregate offering          Amount of
     to be registered             Registered          price per unit (1)          price (1)           registration fee
-------------------------------------------------------------------------------------------------------------------------
<S>                          <C>                      <C>                     <C>                     <C>
Common Stock, par value
$0.01......................       2,000,000                 $ 24.14              $ 48,280,000            $ 12,745.92
-------------------------------------------------------------------------------------------------------------------------
</TABLE>

(1) Estimated solely for the purpose of calculating the registration fee.
    Pursuant to Rule 457(h), the proposed maximum offering price per share is
    based on the average of the high and low price per share of $24.14 on
    September 18, 2000, as reported by the Nasdaq National Market.
================================================================================

<PAGE>

                                    PART I

             INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

    The Section 10(a) prospectus being delivered by ATMI, Inc. (the "Company")
to participants in the Company's 2000 Stock Plan, as required by Rule 428 under
the Securities Act of 1933, as amended (the "Securities Act"), has been prepared
in accordance with the requirements of Form S-8 and relates to shares of Common
Stock, par value $0.01 per share, issued or reserved for issuance pursuant to
awards granted under the 2000 Stock Plan.  The information with respect to
awards granted under the 2000 Stock Plan required in the Section 10(a)
prospectus is included in documents being maintained and delivered by the
Company as required by Rule 428 under the Securities Act.  The Company shall
provide to participants a written statement advising them of the availability
without charge, upon written or oral request, of documents incorporated by
reference herein, as is required by Item 2 of Part I of Form S-8.
<PAGE>

                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

        The following documents are hereby incorporated by reference in this
registration statement:

        (a)  The Company's Annual Report on Form 10-K/A for the year ended
December 31, 1999;

        (b)  The Company's Quarterly Reports on Form 10-Q for the quarters ended
March 31, 2000 and June 30, 2000;

        (c)  The Company's Current Report on Form 8-K/A dated July 7, 2000; and

        (d)  The description of the common stock of the Company's predecessor
registrant, Advanced Technology Materials, Inc. ("ATM"), contained in ATM's
registration statement on Form 8-A filed on October 29, 1993, which description
was amended on Form 8-A/A filed on November 11, 1993, and any amendment or
report filed for the purpose of further updating such description.

        All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), prior to the filing of a post-effective amendment which
indicates that all securities offered hereby have been sold or which deregisters
all such securities then remaining unsold, shall be deemed to be incorporated by
reference in this registration statement and to be part thereof from the date of
filing of such documents.  Any statement contained in a document incorporated or
deemed to be incorporated by reference in this registration statement shall be
deemed to be modified or superseded for purposes of this registration statement
to the extent that a statement contained herein or in any other subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement.  Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this registration statement.

Item 4. Description of Securities.

        This Item is not applicable.


                                     II-1
<PAGE>

Item 5. Interests of Named Experts and Counsel.

        As of the date of this registration statement, 7,000 shares of the
Company's Common Stock are beneficially owned by lawyers employed at Shipman &
Goodwin LLP, counsel to the Company.

Item 6. Indemnification of Directors and Officers.

        The Company's Certificate of Incorporation provides that the personal
liability of the directors of the Company shall be limited to the fullest extent
permitted by the provisions of Section 102(b)(7) of the Delaware General
Corporation Law, as amended (the "DGCL").  Section 102(b)(7) of the DGCL
generally provides that no director shall be liable personally to the Company or
its stockholders for monetary damages for breach of fiduciary duty as a
director; however, the Certificate of Incorporation does not eliminate the
liability of a director for (i) any breach of the director's duty of loyalty to
the Company or its stockholders; (ii) acts or omissions not in good faith or
that involve intentional misconduct or a knowing violation of law; (iii) acts or
omissions in respect of certain unlawful dividend payments or stock redemptions
or repurchases; or (iv) any transaction from which such director derives
improper personal benefit.  The effect of this provision is to eliminate the
rights of the Company and its stockholders (through stockholders' derivative
suits on behalf of the Company) to recover monetary damages against a director
for breach of his or her fiduciary duty of care as a director (including
breaches resulting from negligent or grossly negligent behavior) except in the
situations described in clauses (i) through (iv) above.  The limitations
summarized above, however, do not affect the ability of the Company or its
stockholders to seek nonmonetary remedies, such as an injunction or rescission,
against a director for breach of his or her fiduciary duty.

        In addition, the Company's Certificate of Incorporation provides that
the Company shall, to the fullest extent permitted by Section 145 of the DGCL,
indemnify all persons whom it may indemnify pursuant to Section 145 of the DGCL.
Section 145 of the DGCL permits a company to indemnify an officer or director
who was or is a party or is threatened to be made a party to any proceeding
because of his or her position, if the officer or director acted in good faith
and in a manner he or she reasonably believed to be in or not opposed to the
best interests of the Company and, with respect to any criminal action or
proceeding, had no reasonable cause to believe his or her conduct was unlawful.
Insofar as indemnification for liabilities arising under the Securities Act may
be permitted to directors, officers, or persons controlling the Company pursuant
to the foregoing provisions, the Company has been informed that in the opinion
of the Securities and Exchange Commission, such indemnification is against
public policy as expressed in the Securities Act and is therefore unenforceable.

        The Company maintains insurance for officers and directors against
certain liabilities, including liabilities under the Securities Act. The effect
of this insurance is to indemnify any officer or director of the Company against
expenses, including, without limitation, attorneys' fees, judgments, fines and
amounts paid in settlement, incurred by an officer or director upon a
determination that such person acted in good faith.


                                     II-2
<PAGE>

Item 7. Exemption from Registration Claimed.

        This Item is not applicable.

Item 8. Exhibits.

Exhibit No.         Description
----------          -----------

   4.1(a)  Certificate of Incorporation of the Company (Exhibit 3.01 to the
           Company's Registration Statement on Form S-4, filed September 10,
           1997, Registration No. 333-35323 (the "1997 Form S-4 Registration
           Statement")). (1)

   4.1(b)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           4.1(b) to the Company's Post-Effective Amendment No. 1 to
           Registration Statement on Form S-8, filed October 10, 1997,
           Registration No. 33-77060). (1)

   4.1(c)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           3.01(c) to Amendment No. 2 to ATMI's Registration Statement on Form
           S-4, filed July 1, 1998, Registration No. 333-51333). (1)

   4.2     Bylaws of the Company (Exhibit 3.02 to the 1997 Form S-4 Registration
           Statement). (1)

   5.1     Opinion of Shipman & Goodwin LLP as to the legality of the securities
           being registered. (2)

  23.1     Consent of Shipman & Goodwin LLP (included in Exhibit 5.1). (2)

  23.2     Consent of Ernst & Young LLP. (2)

  23.3     Consent of Deloitte & Touche LLP. (2)

  23.4     Consent of Arthur Andersen LLP. (2)

  23.5     Consent of Rath, Anders, Dr. Wanner and Partner. (2)

  23.6     Consent of Arthur Andersen LLP. (2)

  24.1     Power of Attorney (included in the signature page of this
           registration statement). (2)

  99.1     The Company's 2000 Stock Plan. (2)

__________________________

(1)  Incorporated by reference.

(2)  Filed herewith.

                                     II-3
<PAGE>

Item 9. Undertakings.

        (a)  The undersigned registrant hereby undertakes:

             (1)  To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement.

             (2)  That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

             (3)  To remove from registration by means of post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

        (b)  The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13 or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the registration statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

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

                                     II-4
<PAGE>

                                  SIGNATURES

        Pursuant to requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Danbury, State of Connecticut, on September 19, 2000.

                                 ATMI, INC.


                                 By: /s/ Eugene G. Banucci
                                    ------------------------------------
                                    Eugene G. Banucci
                                    President, Chief Executive Officer
                                    and Chairman of the Board

                                    POWER OF ATTORNEY

        Know All Persons by These Presents, that each person whose signature
appears below constitutes and appoints Eugene G. Banucci, Ph.D. and Daniel P.
Sharkey, and each of them, his true and lawful attorneys-in-fact and agents,
with full power of substitution and resubstitution for him and in his name,
place and stead, in any and all capacities to sign any and all amendments
(including post-effective amendments) to this registration statement, and to
file same, with all exhibits thereto, and other documents in connection
therewith, with full power and authority to do and perform each and every act
and thing requisite or necessary to be done in and about the premises, as fully
to all intents and purposes as he might or could do in person, hereby ratifying
and confirming all that said attorneys-in-fact and agents or any of them, or
their or his substitute or substitutes, may lawfully do or cause to be done by
virtue hereof.

                              ___________________

        Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
            Signature                             Title                                  Date
            ---------                             -----                                  ----
<S>                                      <C>                                     <C>
/s/ Eugene G. Banucci                    President, Chief Executive Officer,       September 19, 2000
--------------------------------             Chairman of the Board and Director
Eugene G. Banucci, Ph.D.                     (principal executive officer)


/s/ Daniel P. Sharkey                    Vice President, Treasurer and Chief       September 19, 2000
--------------------------------             Financial Officer (principal
Daniel P. Sharkey                            financial and accounting officer)


/s/ Mark A. Adley                        Director                                  September 19, 2000
--------------------------------
Mark A. Adley


/s/ Robert S. Hillas                     Director                                  September 19, 2000
--------------------------------
Robert S. Hillas
</TABLE>

                                     II-5
<PAGE>

<TABLE>
<S>                                      <C>                                     <C>
/s/ Stephen H. Mahle                     Director                                  September 19, 2000
--------------------------------
Stephen H. Mahle


/s/ C. Douglas Marsh                     Director                                  September 19, 2000
--------------------------------
C. Douglas Marsh


/s/ Michael J. Yomazzo                   Director                                  September 19, 2000
--------------------------------
Michael J. Yomazzo
</TABLE>
<PAGE>

                                 Exhibit Index
                                 -------------

Exhibit No.         Description
----------          -----------

   4.1(a)  Certificate of Incorporation of the Company (Exhibit 3.01 to the
           Company's Registration Statement on Form S-4, filed September 10,
           1997, Registration No. 333-35323 (the "1997 Form S-4 Registration
           Statement")). (1)

   4.1(b)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           4.1(b) to the Company's Post-Effective Amendment No. 1 to
           Registration Statement on Form S-8, filed October 10, 1997,
           Registration No. 33-77060). (1)

   4.1(c)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           3.01(c) to Amendment No. 2 to ATMI's Registration Statement on Form
           S-4, filed July 1, 1998, Registration No. 333-51333). (1)

   4.2     Bylaws of the Company (Exhibit 3.02 to the 1997 Form S-4 Registration
           Statement). (1)

   5.1     Opinion of Shipman & Goodwin LLP as to the legality of the securities
           being registered. (2)

  23.1     Consent of Shipman & Goodwin LLP (included in Exhibit 5.1). (2)

  23.2     Consent of Ernst & Young LLP. (2)

  23.3     Consent of Deloitte & Touche LLP. (2)

  23.4     Consent of Arthur Andersen LLP. (2)

  23.5     Consent of Rath, Anders, Dr. Wanner and Partner. (2)

  23.6     Consent of Arthur Andersen LLP. (2)

  24.1     Power of Attorney (included in the signature page of this
           registration statement). (2)

  99.1     The Company's 2000 Stock Plan. (2)


______________________

(1)  Incorporated by reference.

(2)  Filed herewith.
[{"type": "S-8", "sequence": "1", "filename": "0001.txt", "description": "FORM S-8", "secsgml_size_bytes": 20377}]
{"company-data": {"conformed-name": "ATMI INC", "cik": "0001041577", "assigned-sic": "2810", "irs-number": "061481060", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-46222", "film-number": "725794"}, "business-address": {"street1": "7 COMMERCE DRIVE", "city": "DANBURY", "state": "CT", "zip": "06810-4169", "phone": "2037941100"}, "mail-address": {"street1": "7 COMMERCE DRVIE", "city": "DANBURY", "state": "CT", "zip": "06810-4169"}, "former-company": {"former-conformed-name": "ATMI HOLDINGS INC", "date-changed": "19970625"}}
As filed with the Securities and Exchange Commission on September 20, 2000

                                                     Registration No. 333-

================================================================================

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

                                   FORM S-8
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
                                ______________

                                  ATMI, INC.
            (Exact name of registrant as specified in its charter)

                     Delaware                                 06-1481060
           (State or other jurisdiction of                 (I.R.S. Employer
            incorporation or organization)                Identification No.)
                                ______________

          7 Commerce Drive, Danbury, Connecticut                  06810
         (Address of Principal Executive Offices)              (Zip Code)
                                ______________

                                  ATMI, Inc.
                                2000 Stock Plan
                           (Full title of the plan)
                                ______________

                               Eugene G. Banucci
                            Chief Executive Officer
                                  ATMI, Inc.
                               7 Commerce Drive
                          Danbury, Connecticut 06810
                    (Name and address of agent for service)
                                ______________

                                (203) 794-1100
         (Telephone number, including area code, of agent for service)
                                ______________

                                   Copy to:

                             Donna L. Brooks, Esq.
                             Shipman & Goodwin LLP
                               One American Row
                          Hartford, Connecticut 06103
                                (860) 251-5000

                       CALCULATION OF REGISTRATION FEE
=========================================================================================================================
                                                                                   Proposed
                                                           Proposed                maximum
    Title of Securities          Amount to be          maximum offering       aggregate offering          Amount of
     to be registered             Registered          price per unit (1)          price (1)           registration fee
-------------------------------------------------------------------------------------------------------------------------
Common Stock, par value
$0.01......................       2,000,000                 $ 24.14              $ 48,280,000            $ 12,745.92
-------------------------------------------------------------------------------------------------------------------------
(1) Estimated solely for the purpose of calculating the registration fee.
    Pursuant to Rule 457(h), the proposed maximum offering price per share is
    based on the average of the high and low price per share of $24.14 on
    September 18, 2000, as reported by the Nasdaq National Market.
================================================================================
PART I

             INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

    The Section 10(a) prospectus being delivered by ATMI, Inc. (the "Company")
to participants in the Company's 2000 Stock Plan, as required by Rule 428 under
the Securities Act of 1933, as amended (the "Securities Act"), has been prepared
in accordance with the requirements of Form S-8 and relates to shares of Common
Stock, par value $0.01 per share, issued or reserved for issuance pursuant to
awards granted under the 2000 Stock Plan.  The information with respect to
awards granted under the 2000 Stock Plan required in the Section 10(a)
prospectus is included in documents being maintained and delivered by the
Company as required by Rule 428 under the Securities Act.  The Company shall
provide to participants a written statement advising them of the availability
without charge, upon written or oral request, of documents incorporated by
reference herein, as is required by Item 2 of Part I of Form S-8.
PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

        The following documents are hereby incorporated by reference in this
registration statement:

        (a)  The Company's Annual Report on Form 10-K/A for the year ended
December 31, 1999;

        (b)  The Company's Quarterly Reports on Form 10-Q for the quarters ended
March 31, 2000 and June 30, 2000;

        (c)  The Company's Current Report on Form 8-K/A dated July 7, 2000; and

        (d)  The description of the common stock of the Company's predecessor
registrant, Advanced Technology Materials, Inc. ("ATM"), contained in ATM's
registration statement on Form 8-A filed on October 29, 1993, which description
was amended on Form 8-A/A filed on November 11, 1993, and any amendment or
report filed for the purpose of further updating such description.

        All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), prior to the filing of a post-effective amendment which
indicates that all securities offered hereby have been sold or which deregisters
all such securities then remaining unsold, shall be deemed to be incorporated by
reference in this registration statement and to be part thereof from the date of
filing of such documents.  Any statement contained in a document incorporated or
deemed to be incorporated by reference in this registration statement shall be
deemed to be modified or superseded for purposes of this registration statement
to the extent that a statement contained herein or in any other subsequently
filed document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement.  Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this registration statement.

Item 4. Description of Securities.

        This Item is not applicable.

                                     II-1
Item 5. Interests of Named Experts and Counsel.

        As of the date of this registration statement, 7,000 shares of the
Company's Common Stock are beneficially owned by lawyers employed at Shipman &
Goodwin LLP, counsel to the Company.

Item 6. Indemnification of Directors and Officers.

        The Company's Certificate of Incorporation provides that the personal
liability of the directors of the Company shall be limited to the fullest extent
permitted by the provisions of Section 102(b)(7) of the Delaware General
Corporation Law, as amended (the "DGCL").  Section 102(b)(7) of the DGCL
generally provides that no director shall be liable personally to the Company or
its stockholders for monetary damages for breach of fiduciary duty as a
director; however, the Certificate of Incorporation does not eliminate the
liability of a director for (i) any breach of the director's duty of loyalty to
the Company or its stockholders; (ii) acts or omissions not in good faith or
that involve intentional misconduct or a knowing violation of law; (iii) acts or
omissions in respect of certain unlawful dividend payments or stock redemptions
or repurchases; or (iv) any transaction from which such director derives
improper personal benefit.  The effect of this provision is to eliminate the
rights of the Company and its stockholders (through stockholders' derivative
suits on behalf of the Company) to recover monetary damages against a director
for breach of his or her fiduciary duty of care as a director (including
breaches resulting from negligent or grossly negligent behavior) except in the
situations described in clauses (i) through (iv) above.  The limitations
summarized above, however, do not affect the ability of the Company or its
stockholders to seek nonmonetary remedies, such as an injunction or rescission,
against a director for breach of his or her fiduciary duty.

        In addition, the Company's Certificate of Incorporation provides that
the Company shall, to the fullest extent permitted by Section 145 of the DGCL,
indemnify all persons whom it may indemnify pursuant to Section 145 of the DGCL.
Section 145 of the DGCL permits a company to indemnify an officer or director
who was or is a party or is threatened to be made a party to any proceeding
because of his or her position, if the officer or director acted in good faith
and in a manner he or she reasonably believed to be in or not opposed to the
best interests of the Company and, with respect to any criminal action or
proceeding, had no reasonable cause to believe his or her conduct was unlawful.
Insofar as indemnification for liabilities arising under the Securities Act may
be permitted to directors, officers, or persons controlling the Company pursuant
to the foregoing provisions, the Company has been informed that in the opinion
of the Securities and Exchange Commission, such indemnification is against
public policy as expressed in the Securities Act and is therefore unenforceable.

        The Company maintains insurance for officers and directors against
certain liabilities, including liabilities under the Securities Act. The effect
of this insurance is to indemnify any officer or director of the Company against
expenses, including, without limitation, attorneys' fees, judgments, fines and
amounts paid in settlement, incurred by an officer or director upon a
determination that such person acted in good faith.

                                     II-2
Item 7. Exemption from Registration Claimed.

        This Item is not applicable.

Item 8. Exhibits.

Exhibit No.         Description
----------          -----------

   4.1(a)  Certificate of Incorporation of the Company (Exhibit 3.01 to the
           Company's Registration Statement on Form S-4, filed September 10,
           1997, Registration No. 333-35323 (the "1997 Form S-4 Registration
           Statement")). (1)

   4.1(b)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           4.1(b) to the Company's Post-Effective Amendment No. 1 to
           Registration Statement on Form S-8, filed October 10, 1997,
           Registration No. 33-77060). (1)

   4.1(c)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           3.01(c) to Amendment No. 2 to ATMI's Registration Statement on Form
           S-4, filed July 1, 1998, Registration No. 333-51333). (1)

   4.2     Bylaws of the Company (Exhibit 3.02 to the 1997 Form S-4 Registration
           Statement). (1)

   5.1     Opinion of Shipman & Goodwin LLP as to the legality of the securities
           being registered. (2)

  23.1     Consent of Shipman & Goodwin LLP (included in Exhibit 5.1). (2)

  23.2     Consent of Ernst & Young LLP. (2)

  23.3     Consent of Deloitte & Touche LLP. (2)

  23.4     Consent of Arthur Andersen LLP. (2)

  23.5     Consent of Rath, Anders, Dr. Wanner and Partner. (2)

  23.6     Consent of Arthur Andersen LLP. (2)

  24.1     Power of Attorney (included in the signature page of this
           registration statement). (2)

  99.1     The Company's 2000 Stock Plan. (2)

__________________________

(1)  Incorporated by reference.

(2)  Filed herewith.

                                     II-3
Item 9. Undertakings.

        (a)  The undersigned registrant hereby undertakes:

             (1)  To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement.

             (2)  That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

             (3)  To remove from registration by means of post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

        (b)  The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13 or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the registration statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

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

                                     II-4
SIGNATURES

        Pursuant to requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Danbury, State of Connecticut, on September 19, 2000.

                                 ATMI, INC.

                                 By: /s/ Eugene G. Banucci
                                    ------------------------------------
                                    Eugene G. Banucci
                                    President, Chief Executive Officer
                                    and Chairman of the Board

                                    POWER OF ATTORNEY

        Know All Persons by These Presents, that each person whose signature
appears below constitutes and appoints Eugene G. Banucci, Ph.D. and Daniel P.
Sharkey, and each of them, his true and lawful attorneys-in-fact and agents,
with full power of substitution and resubstitution for him and in his name,
place and stead, in any and all capacities to sign any and all amendments
(including post-effective amendments) to this registration statement, and to
file same, with all exhibits thereto, and other documents in connection
therewith, with full power and authority to do and perform each and every act
and thing requisite or necessary to be done in and about the premises, as fully
to all intents and purposes as he might or could do in person, hereby ratifying
and confirming all that said attorneys-in-fact and agents or any of them, or
their or his substitute or substitutes, may lawfully do or cause to be done by
virtue hereof.

                              ___________________

        Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by the following persons in the
capacities and on the dates indicated.
Signature                             Title                                  Date
            ---------                             -----                                  ----
/s/ Eugene G. Banucci                    President, Chief Executive Officer,       September 19, 2000
--------------------------------             Chairman of the Board and Director
Eugene G. Banucci, Ph.D.                     (principal executive officer)

/s/ Daniel P. Sharkey                    Vice President, Treasurer and Chief       September 19, 2000
--------------------------------             Financial Officer (principal
Daniel P. Sharkey                            financial and accounting officer)

/s/ Mark A. Adley                        Director                                  September 19, 2000
--------------------------------
Mark A. Adley

/s/ Robert S. Hillas                     Director                                  September 19, 2000
--------------------------------
Robert S. Hillas
II-5
/s/ Stephen H. Mahle                     Director                                  September 19, 2000
--------------------------------
Stephen H. Mahle

/s/ C. Douglas Marsh                     Director                                  September 19, 2000
--------------------------------
C. Douglas Marsh

/s/ Michael J. Yomazzo                   Director                                  September 19, 2000
--------------------------------
Michael J. Yomazzo
Exhibit Index
                                 -------------

Exhibit No.         Description
----------          -----------

   4.1(a)  Certificate of Incorporation of the Company (Exhibit 3.01 to the
           Company's Registration Statement on Form S-4, filed September 10,
           1997, Registration No. 333-35323 (the "1997 Form S-4 Registration
           Statement")). (1)

   4.1(b)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           4.1(b) to the Company's Post-Effective Amendment No. 1 to
           Registration Statement on Form S-8, filed October 10, 1997,
           Registration No. 33-77060). (1)

   4.1(c)  Certificate of Amendment to Certificate of Incorporation (Exhibit
           3.01(c) to Amendment No. 2 to ATMI's Registration Statement on Form
           S-4, filed July 1, 1998, Registration No. 333-51333). (1)

   4.2     Bylaws of the Company (Exhibit 3.02 to the 1997 Form S-4 Registration
           Statement). (1)

   5.1     Opinion of Shipman & Goodwin LLP as to the legality of the securities
           being registered. (2)

  23.1     Consent of Shipman & Goodwin LLP (included in Exhibit 5.1). (2)

  23.2     Consent of Ernst & Young LLP. (2)

  23.3     Consent of Deloitte & Touche LLP. (2)

  23.4     Consent of Arthur Andersen LLP. (2)

  23.5     Consent of Rath, Anders, Dr. Wanner and Partner. (2)

  23.6     Consent of Arthur Andersen LLP. (2)

  24.1     Power of Attorney (included in the signature page of this
           registration statement). (2)

  99.1     The Company's 2000 Stock Plan. (2)

______________________

(1)  Incorporated by reference.

(2)  Filed herewith.