A stack structure including a plurality of gate electrodes is vertically stacked on a substrate and extends in a first direction. A channel structure includes vertical channels penetrating the stack structure and a horizontal channel connecting the vertical channels. The horizontal channel are provided under the stack structure. First lower wiring patterns are disposed between the substrate and the stack structure and electrically connected to the channel structure. Each first lower wiring pattern includes a first portion and a second portion having different widths from each other in the first direction.