A semiconductor device includes a first conductivity type semiconductor substrate, a second conductivity type semiconductor layer which is formed on the semiconductor substrate so as to be in contact with the semiconductor substrate, a first conductivity type body region which is formed in a front surface portion of the semiconductor layer, a second conductivity type source region which is formed in a front surface portion of the body region, a second conductivity type drain region which is formed apart from the body region, a gate insulating film which is formed in a front surface of the semiconductor layer so as to be in contact with the body region, a thick insulating film which is formed integrally with the gate insulating film so as to cover the semiconductor layer between the gate insulating film and the drain region and a gate electrode which is opposite to the body region via the gate insulating film. The body region includes a first portion in which a boundary with the semiconductor layer is in contact with the gate insulating film and a second portion in which a boundary with the semiconductor layer is in contact with the thick insulating film.