A semiconductor memory device includes a substrate comprising a memory cell region and a dummy cell region surrounding the memory cell region, the memory cell region including a plurality of memory cells, a plurality of active regions in the memory cell region, each of the plurality of active regions extending in a long axis direction, the long axis direction being a diagonal direction with respect to a first horizontal direction and a second horizontal direction orthogonal to the first horizontal direction, each of the plurality of active regions having a first width in a short axis direction orthogonal to the long axis direction, and a plurality of dummy active regions in the dummy cell region, each extending in the long axis direction, each of the plurality of dummy active regions having a second width greater than the first width in the short axis direction.