PURPOSE: To control pinch-off voltage easily by forming Al to a gate section and forming Pt successively.

CONSTITUTION: A low-resistance GaAs epitaxial layer 22 is formed on a GaAs substrate 21, the predetermined sections of an insulating protective film 23 shaped on the surface of the layer 22 are removed, and a source electrode 24 and a drain electrode 25 are formed. The film 23 in a gate section is removed, Al 26 is evaporated, and Pt 27 is evaporated. Al and Pt in an unnecessary section are removed through a lift-off method, and the whole is thermally treated within a temperature range of 350∼500°C. Consequently, a reaction is generated on the interface between GaAs and Al, and a novel alloy layer 28 can be formed. Al has adhesion properties better than Pt, and an ideal Schottky junction is shaped easily. Accordingly, the diffusion potential of a Schottky barrier hardly varies, and pinch-off voltage is controlled easily.