A method of operating a semiconductor memory device including a memory cell array and an error correction code (ECC) engine, wherein the memory cell array includes a plurality of memory cells and the ECC engine is configured to perform an error correction operation on data of the memory cell array, may include storing, in a nonvolatile storage, a mapping information indicating physical addresses of normal cells to swap with a portion of fail cells when a first unit of memory cells includes a number of the fail cells exceeding an error correction capability of the ECC engine. The first unit of memory cells of the memory cells may be accessed based on a logical address. The method may include performing a memory operation on the memory cell array selectively based on the mapping information.