A semiconductor device (100) includes a substrate (1) having a semiconductor layer (102); a trench (12) in the semiconductor layer (102); a gate insulating film (11) covering a periphery and an inner surface of the trench (12); a gate electrode (8) including a portion filling the trench (12) and a portion around the trench (12), and provided on the gate insulating film (11); an interlayer insulating film (13) on the gate electrode (8); and a hollow (50) above and around the trench (12), and between the gate electrode (8) and the gate insulating film (11). Above the trench (12), the hollow (50) protrudes inside the trench (12) from a plane extending from an upper surface of the gate insulating film (11) at a portion covering the side surface of the trench (12) with a flat shape.