A semiconductor memory device for performing a refresh operation comprises a memory cell array, a driving control unit, a word line driving unit, a sense amplifier driving unit and a sense amplifier. The memory cell array comprising a plurality of cells stores data. The driving control unit receives a row address and a plurality of command signals to output a word line control signal and a sense amplifier control signal, and sets an enable period of the sense amplifier control signal in response to a refresh signal. The word line driving unit receives the word line control signal to drive a word line. The sense amplifier driving unit receives the sense amplifier control signal to drive a sense amplifier. The sense amplifier senses and amplifies data of the bit line in response to an output signal from the sense amplifier driving unit. In the semiconductor memory device, sensing time is increased at a self-refresh mode, thereby reducing self-refresh current and improving refresh characteristics.