The inventive concepts provide semiconductor memory devices and methods for fabricating the same. The semiconductor memory device may include a plurality of gates vertically stacked on a substrate, a vertical channel filling a channel hole vertically penetrating the plurality of gates, and a memory layer vertically extending on an inner sidewall of the channel. The vertical channel may include a lower channel filling a lower region of the channel hole and electrically connected to the substrate, and an upper channel filling an upper region of the channel hole and contacting the lower channel. The upper channel may extend along the memory layer and the lower channel in the upper region of the channel hole and may have a uniform thickness.