A semiconductor device includes a base body, a stacked body on the base body and a first columnar part. The base body includes a substrate, a first insulating film on the substrate, a first conductive film on the first insulating film, and a first semiconductor part on the first conductive film. The stacked body includes conductive layers and insulating layers stacked alternately in a stacking direction. The first columnar part is provided inside the stacked body and the first semiconductor part. The first columnar part includes a semiconductor body and a memory film between the semiconductor body and conductive layers. The semiconductor body extends in the stacking direction. The first columnar part has a first diameter and a second diameter in a first direction crossing the stacking direction. The first diameter inside the first semiconductor part is larger than the second diameter inside the stacked body.