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Exhibit 99.4
[LETTERHEAD OF CIBC WORLD MARKETS CORP.]
The Board of Directors
Applied Science and Technology, Inc.
90 Industrial Way
Wilmington, MA 01887
Members of the Board:
CIBC World Markets Corp. ("CIBC World Markets") hereby consents to the inclusion
of the opinion letter of CIBC World Markets to the Board of Directors of Applied
Science and Technology, Inc. ("ASTeX") as Annex B-2 to, and to the reference
thereto under the captions "SUMMARY - Opinion of ASTeX Financial Advisor" and
"THE MERGER - Opinion of ASTeX's Financial Advisor" in, the joint Proxy
Statement/Prospectus of ASTeX and MKS Instruments, Inc. ("MKS") relating to the
proposed merger transaction involving ASTeX and MKS. In giving such consent, we
do not admit that we come within the category of persons whose consent is
required under, and we do not admit that we are "experts" for purposes of, the
Securities Act of 1933, as amended, and the rules and regulations promulgated
thereunder.
By: /s/ CIBC World Markets Corp.
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CIBC WORLD MARKETS CORP.
November 13, 2000
