Patent ID: 7038252

Claim:
A semiconductor device, comprising: a first semiconductor layer represented by a composition formula Al x Ga 1-x N (0≦x≦1); a first conductivity type or non-doped second semiconductor layer represented by a composition formula Al y Ga 1-y N (0≦y≦1,x<y) and is formed on the first semiconductor layer; a second conductivity type third semiconductor layer represented by a composition formula Al x Ga 1-x N (0≦x≦1) and is selectively formed above the second semiconductor layer; a gate insulator formed on the third semiconductor layer; a gate electrode formed on the gate insulator; a source electrode electrically connected to the second semiconductor layer; a drain electrode electrically connected to the second semiconductor layer; and a fourth semiconductor layer represented by a composition formula Al z Ga 1-z N (1≦z≦1) and is formed so as to be inserted between the second semiconductor layer and the third semiconductor layer.