Nonvolatile memory devices include at least four cylindrical-shaped channel regions, which extend vertically from portions of a substrate located at respective vertices of at least one rhomboid when viewed in a vertical direction relative to a surface of the substrate. A charge storage layer (e.g., ONO layer) is provided on an outer sidewall of each of the cylindrical-shaped channel regions. In addition, to achieve a high degree of integration, a plurality of vertically-stacked gate electrodes are provided, which extend adjacent each of the cylindrical-shaped channel regions.