A semiconductor memory device includes conductive patterns vertically stacked on the substrate and having pad regions extended further at edge portions of the conductive patterns as the conductive patterns descend from an uppermost conductive pattern to a lowermost conductive pattern, a first contact plug disposed on a first pad region of the lowermost conductive pattern, a buffer conductive pattern disposed on a second pad region positioned above the first pad region, and a second contact plug formed on the buffer conductive pattern.