MOS TYPE SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide an MOS type semiconductor device which does not cause any drop in breakdown voltage or increase in on resistance while reducing the manufacturing cost.SOLUTION: The MOS type semiconductor device comprises a p base region 17 arranged selectively on the surface layer of an ndrift layer 1 and having a base in the shape of a curvature, an n-type first region 6 arranged selectively on the surface layer of the p base region 17, a gate electrode 8 covering the surface of the p base region 17 held between the surface of the n-type first region 6 and the surface of the ndrift layer 1 with a gate insulating film 9 interposed therebetween, and a metal electrode 13 coming into conductive contact with the surface of the n-type first region 6 and the surface of the p base region 17. Net doping concentration of the p base region 17 is in such a shape as having a plurality of well regions.