A semiconductor device includes: a stack structure including conductive patterns and stack insulating layers, which are alternately stacked; a channel structure penetrating the stack structure; a tunnel insulating layer surrounding the channel structure; a cell storage pattern surrounding the tunnel insulating layer; and a dummy storage pattern surrounding the tunnel insulating layer, the dummy storage pattern being spaced apart from the cell storage pattern. The conductive patterns include a select conductive pattern in contact with the tunnel insulating layer.