A method of fabricating an integrated circuit device includes forming on a semiconductor substrate a mold stack that includes a plurality of insulating layers and a plurality of mold layers alternately arranged. A mask pattern including an opening is formed on the mold stack. A channel hole is formed by removing the mold stack exposed through the opening. A sacrificial film is formed on a lateral wall of the mold stack exposed through the channel hole. An oxidation process is performed on the sacrificial film and the mold stack to convert the sacrificial film to a sacrificial oxide film. An etching process is performed to remove the sacrificial oxide film.