A semiconductor device includes a p-type semiconductor substrate, an n-type drift region formed in the p-type semiconductor substrate, and a p-type body region formed in the n-type drift region. A circular gate electrode is formed over a pn junction between sides of the p-type body region and the n-type drift region along the pn junction. An n-type drain region and an n-type source region are formed in the n-type drift region and the p-type body region, respectively, with a part of the gate electrode between.