A semiconductor device includes a cell stack structure including first cell stack layers and stack conductive layers, which are alternately stacked. The semiconductor device also includes a dummy stack structure including first dummy stack layers and second dummy stack layers, which are alternately stacked. The semiconductor device further includes a cell plug penetrating the cell stack structure and a cell chip guard penetrating the dummy stack structure, wherein the cell chip guard surrounds the cell stack structure and the cell plug. A level of a bottom surface of a cell chip guard is substantially equal to that of a bottom surface of the cell plug.