A vertical-type memory device includes a substrate having a cell array region and a connection region disposed adjacent to the cell array region, a plurality of gate electrode layers stacked on the cell array region and the connection region, a plurality of channel structures disposed in the cell array region, a plurality of dummy channel structures disposed in the connection region, and a plurality of slits disposed in the plurality of gate electrode layers in the cell array region. The plurality of gate electrode layers forms a stepped structure in the connection region, the plurality of channel structures penetrates the plurality of gate electrode layers, and the plurality of dummy channel structures penetrates at least one of the plurality of gate electrode layers.