A semiconductor memory device includes a first substrate including a first region and a second region, a stacked structure only on the first region of the first substrate among the first region and the second region of the first substrate, the stacked structure including word lines, an interlayer insulating film covering the stacked structure, a dummy conductive structure inside the interlayer insulating film, the dummy conductive structure extending through the stacked structure to contact the first substrate, and a plate contact plug inside the interlayer insulating film, the plate contact plug being connected to the second region of the first substrate, and a height of an upper surface of the dummy conductive structure being greater than a height of an upper surface of the plate contact plug relative to an upper surface of the first substrate.