VERTICAL SEMICONDUCTOR DEVICES

A vertical semiconductor device includes a substrate, a cell array region and a pad region formed on the substrate, and gate patterns and respective insulation layers. The gate patterns may be stacked in a vertical direction perpendicular to an upper surface of the substrate. Each of the gate patterns may extend in a first direction parallel to the upper surface of the substrate on the cell array region and the pad region of the substrate. The gate patterns may include pads, respectively, at edge portions thereof in the first direction. The respective insulation layers may be between adjacent gate patterns in the vertical direction. The gate patterns and the insulation layer on the pad region may serve as a pad structure, and the pad structure may include a first staircase structure having a stepped shape, a second staircase structure having a stepped shape and disposed below the first staircase structure, a flat surface portion between the first and second staircase structures, and a dummy staircase structure formed on the flat surface portion. The dummy staircase structure may be spaced apart from each of the first and second staircase structures.