A semiconductor device including a first conductor layer, a second conductor layer formed over the first conductor layer, a third conductor layer formed over the second conductor layer, a gate trench which passes through the third conductor layer and is formed in the second conductor layer, a first insulating film formed on an inner wall of the gate trench, a second insulating film formed on the inner wall of the gate trench, a first buried conductor layer formed in the gate trench, a gate electrode formed in the gate trench, a fourth conductor layer of the second conductivity type formed on a lower end of the first buried conductor layer and a lower end of the gate trench, and a fifth conduction layer of the first conductivity type formed over the third conductor layer. The first insulating film is thicker than the second insulating film.