A semiconductor device includes a first electrode, a first semiconductor layer connected to the first electrode, a second semiconductor layer on the first semiconductor layer, a third semiconductor layer on the second semiconductor layer, a fourth semiconductor layer on the third semiconductor layer, a second electrode connected to the third and fourth semiconductor layers, a gate electrode extending from the fourth toward the second semiconductor layer next to the third semiconductor layer, a field plate electrode extending in a direction from the fourth toward the second semiconductor layer next to the second semiconductor layer, and a first insulating film between the field plate electrode and the second semiconductor layer and having a lower end further from the field plate electrode than the first semiconductor layer; the first, second, and fourth semiconductor layers are of a first conductivity type; and the third semiconductor layer is of a second conductivity type.