Methods of manufacturing vertical semiconductor devices may include forming a mold structure including sacrificial layers and insulating interlayers with a first opening formed therethrough. The sacrificial layers and the insulating interlayers may be stacked repeatedly and alternately on a substrate. The first opening may expose the substrate. Blocking layers may be formed by oxidizing portions of the sacrificial layers exposed by the first opening. A first semiconductor layer pattern, a charge trapping layer pattern and a tunnel insulation layer pattern, respectively, may be formed on the sidewall of the first opening. A second semiconductor layer may be formed on the first polysilicon layer pattern and the bottom of the first opening. The sacrificial layers and the insulating interlayers may be partially removed to form a second opening. The sacrificial layers may be removed to form grooves between the insulating interlayers. Control gate electrodes may be formed in the grooves.