A semiconductor device includes first to third semiconductor regions, first to fourth electrodes and a first insulating film. The first insulating film is provided between the third electrode and the first semiconductor region, between the third electrode and the second semiconductor region, between the third electrode and the third semiconductor region, and between the fourth electrode and the first semiconductor region. The first insulating film has a first insulating region, a second insulating region and a third insulating region. A first width in the first insulating region is different from a second width in the second insulating region. The first insulating region and the second insulating region are arranged in the direction. A third width of the third insulating region is constant along the second direction.