A semiconductor device includes a stacked body including conductive layers and first insulating layers which are alternately stacked. The stacked body includes, on at least one side thereof, a staircase portion having stairs formed from the conductive layers and the first insulating layers. A second insulating layer different in material from the first insulating layer is provided on an upper surface of the first insulating layer of the staircase portion. The second insulating layer is away from the conductive layer on the same first insulating layer. A third insulating layer is provided on the staircase portion. Contacts are provided in the first, second, and third insulating layers situated in the respective stairs of the staircase portion. The contacts lead from an upper surface of the third insulating layer to the conductive layer under the first insulating layer.