Semiconductor device

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;
• Ncm 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}/Ncm|, then
• the channel layer is configured to satisfy the following equation:
• yc≧Tch/2
• where Tch is the thickness of the entire channel layer.