Patent ID: 6995397

Claim:
A semiconductor device comprising: a semiconductor substrate; a semiconductor region of a first conductivity type formed in at least a part of the semiconductor substrate; a modulation-doped channel layer formed on the first-conductivity-type semiconductor region, having a non-uniform impurity concentration distribution, and being of a second conductivity type; a gate insulating film formed on the channel layer; a gate electrode formed on the gate insulating film; and a source layer of the second conductivity type formed in the first-conductivity-type semiconductor region so as to be located laterally with respect to the gate electrode, wherein given that y is depth into the channel layer from the surface thereof; N(y), a function of the depth y, is the impurity concentration of the channel layer in the depth direction; N cm is the average impurity concentration of the channel layer; and yc, which is the depth of the center of gravity of the impurity concentration distribution in the depth direction in the channel layer, is given by the following equation: yc=|{∫N ( y )· y·dy}/N cm |, then the channel layer is configured to satisfy the following equation: yc≧T ch /2 where T ch is the thickness of the entire channel layer.