A memory device includes a gate structure including a plurality of gate electrode layers stacked on an upper surface of a substrate, a plurality of vertical holes extending in a direction perpendicular to the upper surface of the substrate to penetrate through the gate structure, and a plurality of vertical structures in the plurality of vertical holes, respectively, each vertical structure of the plurality of vertical structures including an embedded insulating layer, and a plurality of channel layers separated from each other, the plurality of channel layers being outside the embedded insulating layer.