For Immediate Release

      ATMI COMPLETES SALE OF EPITAXIAL SERVICES TO INTERNATIONAL RECTIFIER

      DANBURY, CT -- July 20, 2004 -- ATMI, Inc. (Nasdaq: ATMI), a supplier of
materials and materials packaging to the world's leading semiconductor
manufacturers, today announced that it has completed the previously announced
sale of its specialty epitaxial services business, located in Mesa, Arizona, to
International Rectifier Corporation (NYSE: IRF), a world leader in power
management technology.

      ATMI provides specialty materials and materials packaging to the worldwide
semiconductor industry. As the Source of Semiconductor Process Efficiency, ATMI
helps customers improve wafer yields and lower operating costs. For more
information, please visit atmi.com.

      Statements contained herein that relate to ATMI's future performance,
including, without limitation, statements with respect to ATMI's anticipated
results of operations or level of business for 2004 or any other future period,
are forward-looking statements within the safe harbor provisions of the Private
Securities Litigation Reform Act of 1995. Such statements are based on current
expectations only and are subject to certain risks, uncertainties, and
assumptions, including, but not limited to: changes in semiconductor industry
growth or ATMI's markets; competition, problems, or delays developing and
commercializing new products; problems or delays in integrating acquired
operations and businesses into ATMI; problems or delays associated with any
restructuring activity, or implementing any strategy, including resolution of
the various discontinued elements of ATMI's Technologies segment; and other
factors discussed in ATMI's filings with the Securities and Exchange Commission.
Such risks and uncertainties could cause actual results to differ from those
projected. ATMI undertakes no obligation to publicly update or revise any
forward-looking statements, whether because of new information, future events or
otherwise.

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For more information contact:
      Dean Hamilton
      ATMI
      203.207.9349 Direct
      203.794.1100 x4202
      dhamilton@atmi.com
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