A semiconductor memory device includes a buffer die and a plurality of memory dies. Each of the memory dies includes a memory cell array, an error correction code (ECC) engine and a test circuit. The memory cell array includes a plurality of memory cell rows, each including a plurality of volatile memory cells. The test circuit, in a test mode, generates a test syndrome and an expected decoding status flag indicating error status of the test syndrome, receives test parity data generated by the ECC engine based on the test syndrome and a decoding status flag indicating error status of the test parity data, and determines whether the ECC engine has a defect based on comparison of the test syndrome and the test parity data and a comparison of the expected decoding status flag and the decoding status flag.