Exhibit 8.1

                            [LETTERHEAD OF MANATT]


July 24, 2001

Greater Bay Bancorp
400 Emerson Street
Palo Alto, California 94301

GBB Capital V
400 Emerson Street
Palo Alto, California 94301

     Re:  Material Federal Income Tax Consequences
          of the Purchase and Ownership of Trust Preferred Securities
          Issued by Greater Bay Bancorp

Ladies and Gentlemen:

     We have acted as special counsel to Greater Bay Bancorp and its
subsidiaries ("GBB") 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-3 that is being filed with
the Securities and Exchange Commission on this date (the "Registration
Statement"). The Registration Statement relates to the offer for sale of an
aggregate of between $75 million and $86.25 million liquidation amount of Trust
Preferred Securities, liquidation amount $25 per Trust Preferred Security (the
"Capital Securities") of GBB Capital V, a statutory business trust formed under
the Business Trust Act of the State of Delaware (the "Trust"), guaranteed (the
"Guarantee" and, together with the Capital Securities and the Junior
Subordinated Interest Debentures referred to below, the "Securities") by GBB
pursuant to the Guarantee Agreement (the "Guarantee Agreement") to be entered
into by and between GBB and Wilmington Trust Company, as guarantee trustee (the
"Guarantee Trustee"), the form of which is being filed as an exhibit to the
Registration Statement. GBB will be the owner of all of the undivided beneficial
ownership interests represented by the Common Securities (the "Common
Securities") of the Trust. The Trust will issue the Capital Securities and the
Common Securities to GBB in exchange for Junior Subordinated Interest Debentures
(the "Junior Subordinated Debentures") issued by GBB. The Junior Subordinated
Debentures are to be issued pursuant to an Indenture (the "Indenture") to be
entered into between GBB and Wilmington Trust Company, as indenture trustee (the
"Indenture Trustee"), the form of which is being filed as an exhibit to the
Registration Statement.

     This opinion letter relates to the material federal income tax consequences
of the purchase and ownership of the Capital Securities by investors.  All
capitalized terms used in this


Greater Bay Bancorp
GBB Capital V
July 24, 2001
Page 2


opinion letter and not otherwise defined herein have the same meaning as set
forth in the Indenture.

     We have examined the Registration Statement, the form of the Amended and
Restated Trust Agreement of the Trust, and such other documents as we have
deemed necessary to render our opinions expressed below.  In our examination of
such material, we have relied upon the current and continued accuracy of the
factual matters we have considered, and we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals and
the conformity to original documents of all copies of documents submitted to us.
We assume for purposes of our opinions that there are no agreements or
understandings with respect to the transactions contemplated in the documents
referred to above other than those described therein and that all parties to
such documents will comply with the terms thereof, including all tax reporting
requirements contained therein.  Our opinions are also based (with your consent)
on certain representations from GBB in a letter to us of even date herewith.  In
addition, we also have assumed that the transactions related to the issuance of
the Junior Subordinated Debentures, the Capital Securities and the Guarantee
Agreement will be consummated in accordance with the terms and forms of such
documents and as described in the Registration Statement.

     Based on the foregoing, and assuming the Trust will be maintained in
compliance with the terms of the form of the Amended and Restated Trust
Agreement of the Trust, it is our opinion that more likely than not the
following conclusions would be sustained by a court with jurisdiction in a
properly presented case (with all appeals exhausted):

     (1) The Trust will be classified for United Stated federal income tax
purposes as a grantor trust and not as an association taxable as a corporation
and, as a result, each beneficial owner of Capital Securities will be treated as
owning an undivided beneficial interest in the Junior Subordinated Debentures
held by the Trust.

     (2) The Junior Subordinated Debentures will be classified for federal
income tax purposes as indebtedness of GBB.

     (3) Except in the case of the occurrence of an Extended Interest Payment
Period, stated interest on the Junior Subordinated Debentures will be included
in income by a holder of Capital Securities at the time such interest income is
paid or accrued in accordance with the holder's regular method of tax
accounting. If GBB exercises its right to defer payments of interest on the
Junior Subordinated Debentures during an Extended Interest Payment Period,
beneficial owners of Capital Securities will commence reporting interest income
with respect to the


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GBB Capital V
July 24, 2001
Page 3

Junior Subordinated Debentures under the original issue discount rules of the
Internal Revenue Code of 1986, as amended (the "Code").

     (4) Gain or loss will be recognized by a holder of Capital Securities on a
sale of Capital Securities (including a redemption for cash) in an amount equal
to the difference between the amount realized (which for this purpose will
exclude amounts attributable to accrued interest or original issue discount not
previously included in income) and the holder's adjusted tax basis in the
Capital Securities sold or so redeemed. Gain or loss recognized by the holder on
a sale of Capital Securities held for more than one year will generally be
taxable as long-term capital gain or loss.

     (5) A distribution by the Trust of the Junior Subordinated Debentures, as
described in the Registration Statement (and subject to the limits discussed
therein), will be non-taxable and will result in the distributee receiving
directly its pro rata share of the Junior Subordinated Debentures previously
held indirectly through the Trust, with a holding period and aggregate tax basis
equal to the holding period and aggregate tax basis such distributee had in its
Capital Securities before such distribution.

     (6) The discussion of "Material Federal Income Tax Consequences" in the
Registration Statement accurately describes the material federal income tax
consequences concerning the Capital Securities.

     These opinions are based upon the Code, the Treasury Regulations
promulgated thereunder and other relevant authorities and law, all as in effect
on the date hereof.  Future changes in the law or interpretations of the law may
cause the tax effects of the transactions referred to herein to be materially
different from those described above.  We have undertaken no obligation to
update this opinion in such event.

     Other than the specific tax opinions set forth in this letter, no other
opinion has been requested of us or rendered by us with respect to the tax
treatment of the Junior Subordinated Debentures, the Capital Securities or the
Guarantee Agreement, including, but not limited to, the tax treatment of the
proposed transactions under other provisions of the Code and the Treasury
Regulations or the tax treatment of the proposed transactions under state,
local, foreign or any other tax laws.

     We hereby consent to the filing of this letter as an exhibit to the
Registration Statement and the use of our name in the Registration Statement
under the caption "Material Federal


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GBB Capital V
July 24, 2001
Page 4

Income Tax Consequences." In giving such consent, we do not concede that this
consent is required under Section 7 of the Securities Act of 1933.

                                 Very truly yours,



                                 /s/ Manatt, Phelps & Phillips, LLP

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