A semiconductor device includes a substrate; a stack structure including a first gate layer, a first interlayer insulating layer, and a second gate layer; and a channel structure penetrating through the stack structure and in contact with the substrate, the channel structure including a channel layer, a vertical tunneling layer surrounding the channel layer, a charge storage pattern on an outer surface of the vertical tunneling layer, and a blocking pattern on an outer surface of the charge storage pattern, the charge storage pattern includes first and second charge storage material layers vertically spaced apart and adjacent to the gate layers, the blocking pattern includes vertically spaced blocking material layers between the charge storage material layers and the gate layers, and the blocking pattern contacts the outer surface of the charge storage pattern and includes a vertical protrusion extending longer than the outer surface of the charge storage pattern.