A vertical-type memory device and a manufacturing method thereof, the device including a substrate having a cell array region and a connection region; gate electrode layers stacked on the cell array region and the connection region of the substrate, the gate electrode layers forming a stepped structure in the connection region; a cell channel layer in the cell array region, the cell channel layer passing through the plurality of gate electrode layers; a dummy channel layer in the connection region, the dummy channel layer passing through at least one gate electrode layer of the plurality of gate electrode layers; a cell epitaxial layer disposed below the cell channel layer; and a dummy epitaxial layer disposed below the dummy channel layer, wherein the dummy epitaxial layer has a shape that is different from a shape of the cell epitaxial layer.