EXHIBIT 5



                    [ALPHA INDUSTRIES, INC. LETTERHEAD]






                                                       June 8, 2000

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

      Re:     Network Device Inc. 1997 Stock Option Plan
              Network Device Inc. 1999 Stock Option Plan

Ladies and Gentlemen:

                  I have acted as corporate counsel to Alpha Industries,
Inc., a Delaware corporation (the "Registrant"), in connection with the
preparation of a Registration Statement on Form S-8 (the "Registration
Statement"), for the purpose of registering with the Securities and
Exchange Commission (the "Commission"), under the Securities Act of 1933,
as amended (the "Securities Act"), of an aggregate of 178,731 shares of the
Registrant's common stock, par value $0.25 per share ("Common Stock"),
issuable pursuant to the Network Device Inc. 1997 Stock Option Plan and the
Network Device Inc. 1999 Stock Option Plan (the "Plans"). The Plans
provided for the grant of options to purchase common stock, no par value,
of Network Device Inc. to officers, directors, employees and consultants of
Network Device Inc. However, pursuant to the Agreement and Plan of Merger
among the Registrant, Aries Acquisition Corporation, a Delaware corporation
and wholly owned subsidiary of the Registrant and Network Device Inc.,
dated as of February 10, 2000, these options have each been converted into
an option to purchase a fraction of a share of Common Stock ("Options").

                  This opinion is being furnished in accordance with the
requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

                  In connection with this opinion, I have examined
originals or copies, certified or otherwise identified to my satisfaction,
of (i) the Registration Statement, as filed with the Commission on the date
hereof under the Securities Act; (ii) a specimen certificate representing
the Common Stock; (iii) the Restated Certificate of Incorporation of the
Registrant, as presently in effect; (iv) the Amended and Restated By-Laws
of the Registrant, as presently in effect; (v) certain resolutions of the
Board of Directors of the Registrant relating to the Plans; and (vi) the
Plans. I have also examined originals or copies, certified or otherwise
identified to my satisfaction, of such records of the Registrant and such
other documents, certificates and records as I have deemed necessary or
appropriate as a basis for the opinions set forth herein.

                  In my examination, I have assumed the legal capacity of
all natural persons, the genuineness of all signatures, the authenticity of
all documents submitted to me as originals, the conformity to original
documents of all documents submitted to me as certified, conformed or
photostatic copies and the authenticity of the originals of such copies. In
making my examination of documents executed or to be executed by parties
other than the Registrant, I have assumed that such parties had or will
have the power, corporate or other, to enter into and perform all
obligations thereunder and have also assumed the due authorization by all
requisite action, corporate or other, and execution and delivery by such
parties of such documents and the validity and binding effect thereof on
such parties. As to any facts material to the opinions expressed herein
which I have not independently established or verified, I have relied upon
statements and representations of officers and other representatives of the
Registrant and others. I have assumed that each award agreement setting
forth the terms of each grant of options or other awards under the Plans
will be consistent with the Plans and will be duly authorized and validly
executed and delivered by the parties thereto, and that the consideration
received by the Registrant for the Common Stock delivered pursuant to the
Plans will be in an amount at least equal to the par value of such Common
Stock.

                  I am admitted to the bar in the State of Massachusetts,
and I do not express any opinion as to the laws of any jurisdiction other
than the particular law of the state in which I am admitted to the bar.

                  Based upon and subject to the foregoing, I am of the
opinion that the shares of Common Stock have been duly authorized for
issuance by the Registrant and, when such shares of Common Stock are issued
upon exercise of Options in accordance with the terms of the Plans, such
shares of Common Stock will be validly issued, fully paid and
nonassessable.

                  I hereby consent to the filing of this opinion with the
Commission as an exhibit to the Registration Statement. In giving such
consent, I do not thereby admit that I am included in the category of
persons whose consent is required under Section 7 of the Securities Act or
the rules and regulations of the Commission promulgated thereunder.

                  This opinion is furnished by me, as the Registrant's
corporate counsel, in connection with the filing of the Registration
Statement with the Commission and, except as provided in the immediately
preceding paragraph, is not to be used, circulated, quoted or otherwise
referred to for any other purpose or relied upon by any other person
without my prior written permission.

                                                  Very truly yours,

                                                  /s/ JAMES C. NEMIAH

                                                  JAMES C. NEMIAH