A semiconductor memory device includes a memory cell array, a repair control circuit and a refresh control circuit. The memory cell array includes a plurality of memory cells and a plurality of redundancy memory cells. The repair control circuit receives a repair command and performs a repair operation on a first defective memory cell among the plurality of memory cells during a repair mode. The semiconductor memory device may operate in a repair mode in response to the repair command. The refresh control circuit performs a refresh operation on non-defective ones of the plurality of memory cells during the repair mode.