<PAGE> 1
MINTZ, LEVIN, COHN, FERRIS, GLOVSKY AND POPEO, P.C.
One Financial Center
Boston, Massachusetts 02111
617 542 6000
617 542 2241 fax
Exhibit 23.3
December 6, 2000
The Officers and Directors of Applied Science and Technology, Inc.
90 Industrial Way
Wilmington, MA 01887
We hereby consent to the filing of our opinion as Exhibit 8.2 to the
Registration Statement on Form S-4 filed by MKS Instruments, Inc. (Reg. No.
333-49738) relating to the Agreement and Plan of Merger dated as of October 2,
2000 (the "Merger Agreement"), by and among MKS Instruments, Inc., Mango
Subsidiary Corp., a Delaware corporation, and Applied Science and Technology,
Inc., a Delaware corporation, pursuant to which Mango Subsidiary Corp. will
merge with and into Applied Science and Technology, Inc. (the "Merger"). We
further consent to the use of our name in the Registration Statement in
connection with references to this opinion and the tax consequences of the
Merger. In giving this consent, however, we do not hereby admit that we are in
the category of persons whose consent is required under Section 7 of the
Securities Act of 1933, as amended.
/s/ Mintz, Levin, Cohn, Ferris, Glovsky and
-------------------------------------------
Popeo, P.C.
-----------
MINTZ, LEVIN, COHN, FERRIS,
GLOVSKY and POPEO, P.C.
Boston New York Reston Washington New Haven
