A semiconductor memory device includes a pad for receiving an external signal through a first external pin, a reference voltage pad for receiving an external reference voltage through a second external pin, an internal reference voltage generator configured to generate an internal reference voltage using an external voltage in response to a reference voltage select signal, a reference voltage supply unit for generating the reference voltage select signal in response to a plurality of select signals, and selecting one reference voltage between the external reference voltage and the internal reference voltage to output the selected one as a reference voltage, a buffer for converting an output signal of the pad into an internal voltage level on the basis of the reference voltage, and a signal selector for controlling an internal signal to be inputted/outputted through the reference voltage pad in response to the plurality of select signals.