Patent ID: 8564021

Claim:
A semiconductor device comprising a structure in which a channel layer having a composition represented by the chemical formula: Al x M y Ga 1-x-y N (0≦x<1, 0≦y<1, 0≦x+y<1, where M contains at least one of In and B) is formed above a substrate and a conductive semiconductor layer having a composition represented by the chemical formula: Al p M q Ga 1-p-q N (0≦p<1, 0≦q<1, 0≦p+q<1) is formed between the substrate and the channel layer, wherein a semi-insulating semiconductor layer having a composition represented by the chemical formula: Al r M s Ga 1-r-s N (p<r<1, x<r, 0≦s<1, 0≦r+s<1) is formed between the channel layer and the conductive semiconductor layer, and wherein the composition of the semi-insulating semiconductor layer is varied in the thickness direction of the semi-insulating semiconductor layer so that r=p and s=q are satisfied on the conductive semiconductor layer side, r=x and s=y are satisfied on the channel layer side, and p<r and x<r is satisfied in the intermediate portion between the conductive semiconductor layer side and channel layer side.