Semiconductor device and method for manufacturing same

According to an embodiment, a method for manufacturing a semiconductor device includes forming a gate trench extending into a first semiconductor layer; forming a gate insulating film on an internal wall of the gate trench; forming a polysilicon in the gate trench; etching the polysilicon into the gate trench; forming an interlayer insulating film on the polysilicon; etching the first semiconductor layer so as to project the interlayer insulating film from the first semiconductor layer; forming a second semiconductor layer on the first semiconductor layer; forming a third semiconductor layer on the second semiconductor layer; forming a sidewall contacting a side face of the interlayer insulating film; forming a fourth semiconductor layer of the second conductivity type in the second semiconductor layer; and forming a first electrode electrically connected to the third semiconductor layer and the fourth semiconductor layer.