A three-dimensional semiconductor device is disclosed. The device may include an electrode structure that can include a plurality of electrodes that are stacked on a substrate and extend in a first direction. Vertical structures can penetrate the electrode structure to provide a plurality of columns spaced apart from each other in a second direction crossing the first direction. The plurality of columns can include first and second edge columns located adjacent to respective opposite edges of the electrode structure, and the plurality of columns can include a center column located between the first and second edge columns. Distances between adjacent ones of the plurality of columns can decrease in a direction from the first and second edge columns toward the center column.