The semiconductor memory device includes a bank having a cell array and a sense amplifier. A back bias voltage generating unit supplies a back bias voltage to the cell array of the bank. A negative drive voltage generating unit generates negative driving voltages including a normal pull-up voltage, an overdrive voltage, a normal pull-down voltage, and a negative voltage and supplies the negative driving voltages to the sense amplifier of the bank. A switching unit opens a connection between the back bias voltage generating unit and the negative drive voltage generating unit when in active mode and shares the back bias voltage between the back bias voltage generating unit and the negative drive voltage generating unit when in a refresh mode, in response to an external command.