PURPOSE: To obtain a MIS structure electrode which reduces an interface level density and whose characteristic is excellent by a method wherein, before an insulating film is formed, a sulfur passivation treatment is executed to the surface of a substrate and the insulating film is formed by an ECR-CVD method.

CONSTITUTION: An insulating film 14 is formed on a substrate 11 composed of a III-V compound semiconductor; after that, an electrode material is applied to form a MIS structure electrode 15. In this method, before said insulating film 14 is formed, a sulfur passivation treatment is executed to the surface of the substrate 11, and said insulating film 14 is formed by an ECR-CVD method. For example, an n-type GaAs layer 12 and an n+ type Gaps layer 13 are formed sequentially on a p- type GaAs substrate 11 by an OMVPE method, the n+ GaAs layer 13 in a channel region is etched selectively and the n-type GaAs layer 12 is exposed. Then, a passivation treatment is executed by using an (NH4)2Sx solution; after that, an insulating film 14 such as SiN is formed by an ECR-CVD method; then, an annealing operation is executed at 380 to 520°C; after that, a gate electrode 15 is formed.