A MOS transistor includes a semiconductor substrate of a first conductivity type having a major surface, a source and drain of a second conductivity type formed on the major surface to define a channel region therebetween, and a gate arranged in the channel region via an insulating film. The MOS transistor includes an impurity-implanted region of the first conductivity type located at a substrate portion which is deeper than the channel region and is shifted to a source side from a region corresponding to the channel region.