A semiconductor memory device with improved reliability and a related method are provided. The semiconductor memory device includes a mold structure including a plurality of gate electrodes and a plurality of mold insulating films on a first substrate, a channel structure penetrating the mold structure and crossing a respective level of each of the gate electrodes, a plurality of first insulating patterns in the mold structure, the first insulating patterns including a material different from that of the mold insulating films, and a first through via in the first insulating patterns, the first through via penetrating the first substrate and the mold structure. The gate electrodes include a first word line and a second word line on the first word line. A first distance from the first word line to the first through via is different from a second distance from the second word line to the first through via.