A semiconductor memory device including a substrate; a mold structure including gate electrodes and mold insulating layers stacked in a stair shape, channel structures on the substrate, intersecting the gate electrodes, and passing through the mold structure; cell contacts connected to the gate electrodes; a first interlayer insulating layer on the mold structure and covering the channel structures and cell contacts; first metal patterns connected to the channel structures, an upper surface of the first metal patterns being coplanar with an upper surface of the first interlayer insulating layer; second metal patterns connected to the cell contacts, an upper surface of the second metal patterns being coplanar with the upper surface of the first metal patterns; a first blocking layer along the upper surface of the first interlayer insulating layer, the first metal patterns, and the second metal patterns; and a first dummy vias passing through the first blocking layer.