A semiconductor memory device may include a mold structure that includes mold insulation films and gate electrodes alternately stacked on a first substrate, a channel structure that penetrates the mold structure and intersects the gate electrodes, a block separation region that extends in a first direction parallel to an upper surface of the first substrate and cuts the mold structure, a first dam region and a second dam region spaced apart from each other, that each having a closed loop in a plan view and each cutting the mold structure, pad insulation films in the first and second dam regions that are alternately stacked with the mold insulation films and include a material different from the mold insulation films, and a through via which penetrates through the first substrate, the mold insulation films, and the pad insulation films, in the first dam region but not in the second dam region.