A nonvolatile memory device may include a substrate having a cell region, and a cell device isolation layer on the cell region of the substrate to define a cell active region. A floating gate may include a lower floating gate and an upper floating gate sequentially stacked on the cell active region, and a tunnel insulation pattern may be between the floating gate and the cell active region. A control gate electrode may be on the floating gate, and a blocking insulation pattern may be between the control gate electrode and the floating gate. More particularly, the upper floating gate may include a flat portion on the lower floating gate and a pair of wall portions extending upward from both edges of the flat portion adjacent to the cell device isolation layer. Moreover, a width of an upper portion of a space surrounded by the flat portion and the pair of wall portions may be larger than a width of a lower portion of the space. Related methods are also discussed.