Methods of forming vertical nonvolatile memory devices may include forming an electrically insulating layer, which includes a composite of a sacrificial layer sandwiched between first and second mold layers. An opening extends through the electrically insulating layer and exposes inner sidewalls of the first and second mold layers and the sacrificial layer. A sidewall of the opening may be lined with an electrically insulating protective layer and a first semiconductor layer may be formed on an inner sidewall of the electrically insulating protective layer within the opening. At least a portion of the sacrificial layer may then be selectively etched from between the first and second mold layers to thereby define a lateral recess therein, which exposes an outer sidewall of the electrically insulating protective layer.