According to one embodiment, the semiconductor device includes a first semiconductor layer. The semiconductor device includes a plurality of base regions, the base regions are provided on a surface of the first semiconductor layer. The semiconductor device includes a source region selectively provided on each of surfaces of the base regions. The semiconductor device includes a gate electrode provided via a gate insulating film in each of a pair of trenches, each of the trenches penetrate the base regions from a surface of the source region to the first semiconductor layer. The semiconductor device includes a field plate electrode provided via a field plate insulating film in each of the pair of trenches under the gate electrode. A thickness of a part of the field plate insulating film is greater than a thickness of the gate insulating film.