A semiconductor device includes a channel region of a first conductivity type, a gate insulating film formed on the channel region, a gate electrode formed on the gate insulating film, a first region of a second conductivity type and a second region of the second conductivity type, which are formed along the gate electrode while facing each other with the gate electrode interposed between the first region and the second region, a semiconductor region of the second conductivity type on which the first region, the second region and the channel region are formed, and an element isolation region which surrounds the semiconductor region. The gate electrode extends beyond a boundary portion between the channel region and the element isolation region. A width of the first region is smaller than a width of the second region in a channel width direction of the first region and the second region.