Disclosed is a DRAM including a test mode operation capable of testing whether a plurality of memory cells are defective or not in a short time. The DRAM includes a power-on detection signal generator, a power-on reset signal generator, and a test mode instruction signal generator. The power-on detection signal generator detects application of a power supply voltage and generates a power-on detection signal. The power-on reset signal generator is reset by a power-on reset signal, counts at least once an external RAS signal applied after reset and generates a power-on reset signal. The test mode instruction signal generator detects logic states of an internal RAS signal, an internal CAS signal and an internal W signal applied after the power-on reset and generates a test mode instructing signal.