A semiconductor memory device including a substrate including a first block and a second block each having a cell array region and a connection region, a stack including insulating layers and gate electrodes and extending from the cell array region to the connection region, first cell channel structures in the cell array region of the first block and passing through the stack to be electrically connected to the substrate, first dummy channel structures in the connection region of the first block and passing through the stack, second cell channel structures in the cell array region of the second block and passing through the stack, and second dummy channel structures in the connection region of the second block and passing through the stack may be provided. The first dummy channel structures are electrically insulated from the substrate, while the second dummy channel structures are electrically connected to the substrate.