A three-dimensional semiconductor memory device may include a source structure on a substrate, a stack structure including electrode layers and inter-electrode insulating layers, which are on the source structure and are alternately stacked, a vertical structure penetrating the stack structure and the source structure and being adjacent to the substrate, and a separation insulation pattern penetrating the stack structure and the source structure and being spaced apart from the vertical structure. The uppermost one of the inter-electrode insulating layers may include a first impurity injection region located at a first height from a top surface of the substrate. The stack structure may define a groove, in which the separation insulation pattern is located. An inner sidewall of the groove may define a recess region, which is located at the first height from the top surface of the substrate and is recessed toward the vertical structure.