A semiconductor device has a substrate that includes a cell array region and a dummy pattern region surrounding the cell array region. The cell array region includes a cell structure having a plurality of cell active pillars extending in a vertical direction from the cell array region of the substrate and includes cell gate patterns and cell gate interlayer insulating patterns alternately stacked on the substrate. The cell gate patterns and cell gate interlayer insulating patterns have sides facing the cell active pillars. The dummy pattern region includes a damp-proof structure.