- Statement of Ownership (SC 13G)

United States
Securities and Exchange Commission
Washington, DC 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No. __________)

Name of Issuer: ATMI, Inc.

Title of Class of Securities: Common Stock

CUSIP Number: 00207R101 (A fee is not required only if the filing person; (1) has a previous statement on file reporting beneficial ownership of more than five percent of the class of securities described in Item 1; and (2) has filed no amendment subsequent thereto reporting beneficial ownership of five percent or less or such class.) (See Rule 13d-7. 1. Name of Reporting Person Kalmar Investments Inc. 2. Check the appropriate line if a member of a group. (a) __________ (b)__________ 3. SEC USE ONLY 4.Citizenship or place of Organization: Barley Mill House 3701 Kennett Pike Wilmington, DE 19807 Number of 5. Sole Voting Power 1,520,759 Shares Beneficially 6. Shared Voting Power -0- Owned by each Reporting person 7. Sole Dispositive Power 1,520,759 with 8. Shared Dispositive Power -0- 9. Aggregate amount beneficially owned by each reporting person: -0- 10. Check line ___________if the aggregate amount in Row (9) excludes certain shares* 11. Percent of Class represented by amount in Row 9: 4.73 12. Type of Reporting Person: IA Item 1. (a)Issuer: ATMI, Inc (b) Address of Issuer's Principal Executive Offices: 7 Commerce Dr Danbury, CT 06810 Item 2. (a) Name of Person Filing: Kalmar Investments Inc. (b) Address of Principal Business Office: 3701 Kennett Pike, Wilmington, DE 19807 (c) Citizenship: USA (d) Title of Class of Securities:Common Stock (e) CUSIP Number: 00207R101 Item 3. If this statement if filed pursuant to Rule 13d-1(b), or 13d-2(b), check whether the person filing is: (a)___ Broker or Dealer registered under Section 15 of the Act (b)___ Bank as defined in section 3(a)(6)of the Act (c)___ Insurance Company as defined in section 3(a)(19) of the Act (d)___ Investment Company registered under section 8 of the Investment Company Act (e)__X Investment Adviser registered under section 203 of the Investment Advisers Act of 1940 (f)___ Employee Benefit Plan, Pension Fund which is subject to the provisions of the Employee Retirement Income Security Act of 1974 or Endowment Fund (g)___Parent Holding company,in accordance with 240.13d-1(b)(ii)(G)Note: See Item 7 (h)Group, in accordance with 240.13d-1(b)(1)(ii)(H) Item 4. Ownership (a) Amount Beneficially Owned: 1,520,759 (b) Percent of Class: 4.73 (c) number of shares as to which such person has: (i) sole power to vote or to direct the vote: 1,520,759 (ii) shared power to vote or to direct the vote: (iii)sole power to dispose or to direct the disposition of: 1,520,759 (iv) shared power to dispose or to direct the disposition of: Item 10. Certification The following certification shall be included if the statement if filed pursuant to Rule 13d-1(b): I certify below that, to be best of my knowledge and belief, the securities referred to above were acquired in the ordinary course of business and were not acquired for the purpose of and do not have the effect of changing or influencing the control of the issuer of such securities and were not acquired in connection with or as a participant in any transaction having such purposes or effect. After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.