A semiconductor memory device includes a substrate including a memory cell region in which active regions are defined, a peripheral region in which a logic active region is defined, and a boundary region including a region isolation trench between the memory cell region and the peripheral region, a boundary structure including a boundary isolation layer, a region isolation structure, and a region isolation filling layer sequentially disposed in the region isolation trench, and a word line extending across the active regions, wherein among the active regions, an active region located at an outermost part of the memory cell region and the region isolation structure are spaced apart from each other by a first width, and the word line extends by an extension length less than the first width from an edge of the active region located at the outermost part of the memory cell region towards the region isolation structure.