An AlN layer (2), a GaN buffer layer (3), a non-doped AlGaN layer (4a), an n-type AlGaN layer (4b), an n-type GaN layer (5), a non-doped AlN layer (6) and an SiN layer (7) are sequentially formed on an SiC substrate (1). At least three openings are formed in the non-doped AlN layer (6) and the SiN layer (7), and a source electrode (8a), a drain electrode (8b) and a gate electrode (19) are evaporated in these openings.