Disclosed are a memory device including a vertical stack structure and a method of manufacturing the memory device. The memory device includes an insulating structure having a shape including a first surface and a protrusion portion protruding in a first direction from the first surface, a recording material layer covering the protrusion portion along a protruding shape of the protrusion portion and extending to the first surface on the insulating structure a channel layer on the recording material layer along a surface of the recording material layer, a gate insulating layer on the channel layer, and a gate electrode formed at a location on the gate insulating layer to face a second surface which is a protruding upper surface of the protrusion portion, wherein a void exists between the gate electrode and the insulating structure, defined by the insulating structure and the recording material layer.