Integrated circuit devices may include a plurality of word line structures and a plurality of insulating films that are stacked alternately. Sides of the plurality of word line structures and the plurality of insulating films define a side of a channel hole extending through the plurality of word line structures and the plurality of insulating films. The devices may also include a blocking dielectric film on the side of the channel hole, and a plurality of charge storage films on the blocking dielectric film and on the sides of the plurality of word line structures, respectively. Each of the plurality of charge storage films may include a first charge storage film and a second charge storage film sequentially stacked on a respective one of the sides of the plurality of word line structures. A surface of the second charge storage film may include a recess in a middle portion thereof.