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                                                                       EXHIBIT 5
              Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
                             One Financial Center
                         Boston, Massachusetts  02111

                                                      Telephone:  (617) 542-6000
                                                      Facsimile:  (617) 542-2241

                                        October 25, 1999

    Applied Science and Technology, Inc.
    35 Cabot Road
    Woburn, Massachusetts  01801

    Ladies and Gentlemen:

          We have acted as counsel to Applied Science and Technology, Inc., a
    Delaware corporation (the "Company"), in connection with the preparation and
    filing with the Securities and Exchange Commission of a Registration
    Statement on Form S-3 (the "Registration Statement"), pursuant to which the
    Company is registering under the Securities Act of 1933, as amended, a total
    of 325,873 shares (the "Shares") of its common stock, $.01 par value per
    share (the "Common Stock"), for resale to the public.  The Common Stock is
    to be sold by the selling stockholders identified in the Registration
    Statement.  This opinion is being rendered in connection with the filing of
    the Registration Statement.

          In connection with this opinion, we have examined the Company's
    Certificate of Incorporation and By-Laws, both as currently in effect; such
    other records of the corporate proceedings of the Company and certificates
    of the Company's officers as we have deemed relevant; and the Registration
    Statement and the exhibits thereto.

          In our examination, we have assumed the genuineness of all signatures,
    the legal capacity of natural persons, the authenticity of all documents
    submitted to us as originals, the conformity to original documents of all
    documents submitted to us as certified or photostatic copies and the
    authenticity of the originals of such copies.

          Based upon the foregoing, we are of the opinion that (i) the Common
    Stock has been duly and validly authorized by the Company and (ii) the
    Common Stock is duly and validly issued, fully paid and non-assessable.

          Our opinion is limited to the federal securities laws of the United
    States, the laws of the Commonwealth of Massachusetts and the corporate laws
    of the State of Delaware, and we express no opinion with respect to the laws
    of any other jurisdiction.  No opinion is expressed herein with respect to
    the qualification of the Shares under the securities or blue sky laws of any
    state or any foreign jurisdiction.

          We understand that you wish to file this opinion as an exhibit to the
    Registration Statement, and we hereby consent thereto.  We hereby further
    consent to the reference to us under the caption "Legality of Common Stock"
    in the prospectus included in the Registration Statement.

                                           Very truly yours,

                                           /s/ Mintz, Levin, Cohn, Ferris,
                                            Glovsky and Popeo, P.C

                                           MINTZ, LEVIN, COHN, FERRIS,
    cc: Board of Directors                 GLOVSKY and POPEO, P.C.