Three-dimensional semiconductor memory devices are provided. A three-dimensional semiconductor memory device includes a stack structure that includes gate electrodes on a substrate. The three-dimensional semiconductor memory device includes a first vertical structure, a second vertical structure, a third vertical structure, and a fourth vertical structure that penetrate the stack structure and are sequentially arranged in a zigzag shape along a first direction. Moreover, the three-dimensional semiconductor memory device includes a first bit line that extends in the first direction. The first bit line vertically overlaps the second vertical structure and the fourth vertical structure. Centers of the second and fourth vertical structures are spaced apart at the same distance from the first bit line. The first vertical structure is spaced apart at a first distance from the first bit line. The third vertical structure is spaced apart at a second distance from the first bit line.