A memory device includes a peripheral circuit region comprising a first substrate, a plurality of metal layers over the first substrate, and a first metal pad, a cell region comprising a second substrate, a plurality of gate lines over the second substrate, a plurality of upper interconnection layers in the second substrate, and a second metal pad, wherein the cell region is vertically connected to the peripheral circuit region by the first metal pad and the second metal pad, a common source line between the second substrate and the plurality of gate lines, the common source line comprising a through hole, and a word line cut region extending across the plurality of gate lines and extending through the through hole of the common source line to be connected to a first upper interconnection layer from among the plurality of upper interconnection layers.