A semiconductor memory device is capable of maintaining a predetermined back-bias voltage level regardless of operation modes of the semiconductor memory device, by generating a back-bias voltage with driving force changed according to the operation modes. The semiconductor memory device includes an active pumping control signal generating unit for generating an active pumping control signal in response to a plurality of active signals, a voltage detecting unit for detecting a voltage level of a back-bias voltage terminal to output a detection signal, an oscillator for generating an oscillation signal oscillating at a predetermined frequency in response to the detection signal, and a charge pumping unit for performing a charge pumping operation in response to the oscillation signal by controlling a force of driving the back-bias voltage terminal in response to the active pumping control signal.