A nonvolatile memory device comprises a first semiconductor layer including, an upper substrate, and a memory cell array in which a plurality of word lines on the upper substrate extend in a first direction and a plurality of bit lines extend in a second direction. The nonvolatile memory device comprises a second semiconductor layer under the first semiconductor layer in a third direction perpendicular to the first and second directions, the second semiconductor layer including, a lower substrate, and a substrate control circuit on the lower substrate and configured to output a bias voltage to the upper substrate. The second semiconductor layer is divided into first through fourth regions, each of the first through fourth regions having an identical area, and the substrate control circuit overlaps at least a portion of the first through fourth regions in the third direction.