A three-dimensional semiconductor memory device including a substrate including a cell array region and a first connection region arranged in a first direction; and a first block structure on the substrate, the first block structure including a lower stack including a plurality of lower electrodes vertically stacked on the substrate; and intermediate stacks exposing the lower stack, the intermediate stacks including a plurality of intermediate electrodes vertically stacked on the lower stack, wherein, on the cell array region, the first block structure has a first width in a second direction crossing the first direction, and wherein, on the first connection region, the first block structure has a second width, which is larger than the first width, in the second direction.