A non-volatile memory device having a vertical structure includes: a first interlayer insulating layer on a substrate; a first gate electrode disposed on the first interlayer insulating layer; second interlayer insulating layers and second gate electrodes alternately stacked on the first gate electrode; an opening portion penetrating the first gate electrode, the second interlayer insulating layers, and the second gate electrodes and exposing the first interlayer insulating layer; a gate dielectric layer covering side walls and a bottom surface of the opening portion; and a channel region formed on the gate dielectric layer, and penetrating a bottom surface of the gate dielectric layer and the first interlayer insulating layer and thus electrically connected to the substrate, wherein a separation distance between side walls of the gate dielectric layer in a region which contacts the first gate electrode is greater than that in a region which contacts any one of the second gate electrodes.