P-type active region 12; n-type source / drain regions 13a and 13b; gate insulating film 14 made of a
thermal oxide film; gate
electrode 15; source / drain electrodes 16a and 16b, are provided over a p-type
SiC substrate 11. In the active region 12, p-type heavily doped
layers 12a, which are thin enough to create a
quantum effect, and thick undoped
layers 12b are alternately stacked. When carriers flow, scattering of
impurity ions in the active region is reduced, and the channel mobility increases. In the OFF state, a depletion layer expands throughout the active region, and the
breakdown voltage increases. As a result of reduction in charges trapped in the gate insulating film or near the interface between the gate insulating film and the active region, the channel mobility further increases.