A semiconductor device includes a first conductivity type well region formed by counter doping; a transistor having source and drain regions having a second conductivity type, at least one of the regions being arranged in the well region; a LOCOS region arranged around the at least one region in the well region; and a channel stop region having the first conductivity type arranged under the LOCOS region. The at least one region is arranged at a distance from a tip of a bird's beak of the LOCOS in a direction parallel to a channel width of the transistor. The channel stop region is arranged at a distance from the tip of the bird's beak at an opposite side to the at least one region.