A semiconductor memory device includes a first substrate; active or passive circuits on the first substrate; a second substrate above the active or passive circuits; gate electrodes stacked on the second substrate to be spaced apart from each other in a first direction; channel structures penetrating through the gate electrodes and extending in the first direction, and each including a channel layer; separation regions penetrating through the gate electrodes and extending in a second direction; a through-contact plug extending through the second substrate in the first direction and electrically connecting the gate electrodes and the active or passive circuits to each other; and a barrier structure spaced apart from the through-contact plug and surrounding the through-contact plug and having first regions each having a first width, and second regions each having a second width greater than the first width.