Poway-based Cohu, a supplier of test handling and thermal testing hardware used in the semiconductor industry, said Monday that chairman Charles A. Schwan has resigned, and has been replaced by James A. Donahue. Donahue is the firm's President and CEO, and has been a director since 1999. Reason for the resignation was not given, however, Schwan had been CFO and CEO of Cohu, and was Chairman since 2000; he had served at Cohu for 38 years.