content: <PAGE>
  
                        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
  <PAGE>
  
  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
  <PAGE>
  
                                    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
  <PAGE>
  
                                   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
metadata_documents: [{"type": "8-K", "sequence": "1", "description": "FORM 8-K", "secsgml_size_bytes": 2966}]
metadata_filer: {"company-data": {"conformed-name": "GREATER BAY BANCORP", "cik": "0000775473", "assigned-sic": "6021", "irs-number": "770387041", "state-of-incorporation": "CA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "8-K", "act": "34", "file-number": "000-25034", "film-number": "99714219"}, "business-address": {"street1": "2860 WEST BAYSHORE ROAD", "city": "PALO ALTO", "state": "CA", "zip": "94303", "phone": "4153751555"}, "mail-address": {"street1": "2860 BAYSHORE ROAD", "street2": "420 COWPER ST", "city": "PALO ALTO", "state": "CA", "zip": "943011504"}, "former-company": [{"former-conformed-name": "MID PENINSULA BANCORP", "date-changed": "19941031"}, {"former-conformed-name": "SAN MATEO COUNTY BANCORP", "date-changed": "19920703"}]}
text: 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