SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549


                                   FORM 8-K


                            Current Report Pursuant
                         to Section 13 or 15(d) of the
                        Securities Exchange Act of 1934

     Date of Report (Date of earliest event reported): September 15, 1999


                              Greater Bay Bancorp
            (Exact name of registrant as specified in its charter)



      California                                       77-0387041
(State or other jurisdiction of                     (I.R.S. employer
incorporation or organization)                   identification number)



                        Commission file number: 0-25034


                            2860 West Bayshore Road
                          Palo Alto, California 94303
             (Address of principal executive offices and zip code)


      Registrant's telephone number, including area code: (650) 813-8200


Item 5. Other Events.

     On September 15, 1999, Greater Bay Bancorp (the "Registrant") entered into
an Agreement and Plan of Reorganization with Mt. Diablo Bancshares ("MDB")
providing for the merger of MDB with and into the Registrant (the "Merger"),
subject to the terms and conditions therein, including the receipt of all
required regulatory approvals and the approval of the shareholders of MDB.
Following consummation of the Merger, Mt. Diablo National Bank, a wholly owned
subsidiary of MDB, will become a wholly owned subsidiary of the Registrant.

Item 7. Financial Statements and Exhibits.

Exhibits
- --------

 2      Agreement and Plan of Reorganization, dated as of September 15, 1999, by
        and between Greater Bay Bancorp and Mt. Diablo Bancshares

99.1    Press Release dated September 15, 1999

                                       2


                                  SIGNATURES

          Pursuant to the requirements of the Securities Exchange Act of 1934,
     as amended, the Registrant has duly caused this report to be signed on its
     behalf by the undersigned hereunto duly authorized.

                                   Greater Bay Bancorp
                                   (Registrant)



Dated: September 17, 1999          By:   /s/ Linda M. Iannone
                                         --------------------
                                         Linda M. Iannone
                                         Senior Vice President and General
                                         Counsel

                                       3


                                 Exhibit Index
                                 -------------

 2    Agreement and Plan of Reorganization, dated as of September 15, 1999, by
      and between Greater Bay Bancorp and Mt. Diablo Bancshares

99.1  Press Release dated September 15, 1999

                                       4