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                                                                       EXHIBIT 5

                                    January 22, 1999


Alpha Industries, Inc.
20 Sylvan Road
Woburn, MA 01801

     Re:  Alpha Industries, Inc.
          Registration Statement on Form S-8
          ----------------------------------

Gentlemen:

     We are counsel for Alpha Industries, Inc. (the "Company"). We have been
asked to deliver this opinion in connection with the preparation and filing with
the Securities and Exchange Commission under the Securities Act of 1933, as
amended (the "Act"), of a Registration Statement on Form S-8 (this "Registration
Statement") relating to 1,400,000 shares of the Company's Common Stock, $.25 par
value per share (the "Shares"). This opinion letter, together with Schedule A
attached hereto (this "Opinion Letter"), is being rendered in connection with
the filing of the Registration Statement.

     The 1,400,000 Shares covered by the Registration Statement are issuable
under the Company's 1996 Long-Term Incentive Plan, as amended the ("Plan").

     In connection with this Opinion Letter, we have examined and are familiar
with originals or copies, certified or otherwise identified to our satisfaction,
of the following documents (collectively, the "Documents"):

     1.  a certificate from the Secretary of State of the State of Delaware
dated January 19, 1999 as to the legal existence and good standing of the
Company;

     2.  a copy of the Restated Certificate of Incorporation of the Company, as
amended to date, and a certificate of the Secretary that there have been no
further amendments thereto;

     3.  a copy of the By-laws of the Company, as amended to date, certified by
the Secretary of the Company as presently being in effect;

     4.  the corporate minute books or other records of the Company pertaining
to the proceedings of the stockholders and directors of the Company;

     5.  the Plan;
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     6.  a letter from the Company's transfer agent as to the issued and
outstanding shares of the Company's Common Stock, $.25 par value per share; and

     7.  the Registration Statement.

     We have assumed, for the purposes of our opinion herein, that any
conditions to the issuance of the Shares under the Plan have been or will be
satisfied in full.

     We have, without independent investigation, relied upon the representations
and warranties of the various parties as to matters of objective fact contained
in the Documents.

     In addition, this Firm, in rendering legal opinions, customarily makes
certain assumptions which are described in Schedule A hereto. In the course of
our representation of the Company in connection with the preparation of the
Registration Statement, nothing has come to our attention which causes us to
believe reliance upon any of these assumptions is inappropriate, and, with your
concurrence, the opinions hereafter expressed are based upon those assumptions.
The Enumerated Party referred to in Schedule A is the Company.

     We have not made any independent review or investigation of orders,
judgments, rules or other regulations or decrees by which the Company or any of
its property may be bound, nor have we made any independent investigation as to
the existence of actions, suits, investigations or proceedings, if any, pending
or threatened against the Company.

     With your concurrence, our opinion hereafter expressed is based solely upon
(1) our review of the Documents, (2) discussions with those of our attorneys who
have devoted substantive attention to the preparation of the Registration
Statement, and (3) such review of published sources of law as we have deemed
necessary.

     Our opinions contained herein are limited to the laws of the Commonwealth
of Massachusetts, the General Corporation Law of the State of Delaware and the
Federal law of the United States of America.

     We express no legal opinion upon any matter other than those explicitly
addressed below, and our express opinion therein contained shall not be
interpreted to be an implied opinion upon any other matter.

     Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized and, when issued and paid for in accordance
with the terms and conditions of the Plan, the Shares will be validly issued,
fully paid, and non-assessable.


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     We hereby consent to the reference to this firm in the Registration
Statement and to the filing of this opinion as Exhibit 5 to the Registration
Statement.

                                    Very truly yours,

                                    BROWN, RUDNICK, FREED & GESMER, P.C.

                                    By: /s/ Steven R. London
                                        -------------------------------------
                                        Steven R. London, a Member




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                                   SCHEDULE A

                         BROWN, RUDNICK, FREED & GESMER
                              STANDARD ASSUMPTIONS

     In rendering legal opinions, Brown, Rudnick, Freed & Gesmer makes certain
customary assumptions described below:

1.   Each natural person executing any of the Documents has sufficient legal
     capacity to enter into such Documents.

2.   Each Document is accurate, complete and authentic, each original is
     authentic, each copy conforms to an authentic original and all signatures
     are genuine.

3.   All official public records are accurate, complete and properly indexed and
     filed.

4.   There has not been any mutual mistake of fact or misunderstanding, fraud,
     duress, or undue influence by or among any of the parties to the Documents.

5.   The conduct of the parties to the Documents has complied in the past and
     will comply in the future with any requirement of good faith, fair dealing
     and conscionability.

6.   The Enumerated Party will obtain all permits and governmental approvals
     required in the future and take all actions similarly required relevant to
     its performance of its obligations under the Documents.

7.   All parties to or bound by the Documents will act in accordance with, and
     will refrain from taking any action that is forbidden by, the terms and
     conditions of the Documents.

8.   There are no agreements or understandings among the parties to or bound by
     the Documents, and there is no usage of trade or course of prior dealing
     among such parties, that would define, modify, waive, or qualify the terms
     of any of the Documents.