A semiconductor memory device includes a substrate including active regions, word lines in the substrate and each extending in a first direction parallel to an upper surface of the substrate, bit line structures connected to the active regions, respectively, and each extending in a second direction crossing the first direction, and spacer structures on sidewalls of respective ones of the bit line structures. Each of the spacer structures includes a first spacer, a second spacer, and a third spacer. The second spacer is disposed between the first spacer and the third spacer and includes a void defined by an inner surface of the second spacer. A height of the second spacer is greater than a height of the void.