A semiconductor memory device may include a substrate including a first and a second block region, and a stacked structure including insulating films and gate electrodes alternately stacked on the substrate. A vertical channel structure, a word line cut structure, and a block cut structure may penetrate the stacked structure. The word line cut structure may extend in a second direction. The block cut structure may extend in a first direction, connect to the word line cut structure, and define the first and second block regions. The block cut structure may include a first portion connected to the word line cut structure and a second portion connected to the first portion. From a planar viewpoint, the first portion may include at least a part not overlapping the second portion in the first direction and at least a region not overlapping the word line cut structure in the first direction.