PURPOSE: To accurately control a threshold value voltage of a MESFET and to improve its yield by forming a gate electrode of a high melting point metal alloy film of a different material on the same operating layer, and annealing to activate it.

CONSTITUTION: Si ions are implanted in a semi-insulating GaAs substrate 1 with resist 10 as a mask to form an operating layer 2. Then, after the entire surface is covered with a WSi film 3, a region to become an E-FET is removed by etching. Then, after the entire surface is covered with an WSiN film 4, the films 3, 4 are etched with the resist 10 as a mask, and gate electrodes of an E-FET and a D-FET are simultaneously formed. Subsequently, with the resist 10 and the gate electrode as masks Si ions are implanted, and a high concentration layer 5 is formed by a self-alignment method. And, an insulating film 11 is deposited on the entire surface, heat-treated as prescribed with it as an anneal protective film, and the implanted impurity is activated. Further, predetermined parts of the film 11 is opened, and a source electrode 6, a drain electrode 7 are formed of predetermined alloy.