PURPOSE: To provide a GaAs MESFET for excellent microwave band without fluctuating the drain current during the measuring step of DC and high-frequency at all by a method wherein a heat-resistant Schottky metal deposited on the surface of a compound semiconductor substrate exposed in an aperture part formed on an insulating film is to be heat-treated at the temperature within specific range.

CONSTITUTION: An insulating film 2 deposited on one main surface of a compound semiconductor substrate 1 is etched away by RIE step so as to form an aperture part on a prospective Schottky gate region. Next, a heat-resistant Schottky metal 4 deposited on the surface of the compound semiconductor substrate 1 exposed in the aperture part is heat-treated at 500-600°C. For example, a silicon oxide film 2 deposited on the GaAs substrate 1 is etched away by RIE step and then heat-treated in Ar atmosphere at 400-500°C to recover the RIE damage. Next, the Schottky metal 4 comprising WSi is deposited and after the heat treatment in Ar atmosphere at 500-600°C, Ti-Au is deposited and etched away to form a gate electrode 5.