Patent ID: 8487327

Claim:
A III-nitride semiconductor device comprising: a support base comprising a III-nitride semiconductor and having a primary surface, the primary surface extending along a first reference plane perpendicular to a reference axis, the reference axis being inclined at a predetermined angle with respect to a c-axis of the III-nitride semiconductor; and an epitaxial semiconductor region provided on the primary surface of the support base, the epitaxial semiconductor region comprising GaN-based semiconductor layers, the reference axis being inclined at a first angle in a range of not less than 10 degrees and less than 80 degrees with respect to the c-axis of the III-nitride semiconductor toward a first crystal axis, the first crystal axis being either one of m-axis and a-axis of the III-nitride semiconductor, the reference axis being inclined at a second angle in a range of not less than −0.30 degrees and not more than +0.30 degrees with respect to the c-axis of the III-nitride semiconductor toward a second crystal axis, the second crystal axis being another of the m-axis and a-axis, a morphology of an outermost surface of the epitaxial semiconductor region including plural pits, and a pit density of the pits being not more than 5×10 4 cm −2 .