A vertical semiconductor device includes a conductive pattern structure in which insulation patterns and conductive patterns alternately and repeatedly stacked on the substrate. The conductive pattern structure includes an edge portion having a stair-stepped shape. Each of the conductive patterns includes a pad region corresponding to an upper surface of a stair in the edge portion. A pad conductive pattern is disposed to contact a portion of an upper surface of the pad region. A mask pattern is disposed on an upper surface of the pad conductive pattern. A contact plug penetrates the mask pattern to contact the pad conductive pattern.