An internal reference voltage generating circuit that reduces a standby current and the number of pins of a semiconductor memory device, in which a reference voltage is provided to an input buffer that receives a signal through an input to which an on die transmitor resistor is connected, includes: a voltage dividing circuit outputting the reference voltage by a power voltage; a pull down driver connected to an end of the voltage dividing circuit; and a calibration control circuit comparing a voltage level of the input and a voltage level of an end of the voltage dividing circuit, and controlling the on resistor value of the pull down driver according to a result of the comparison. The internal reference voltage generating circuit is operated while the memory controller inputs a signal into a mode register set (MRS) to enable the internal reference voltage generating circuit and the output signal of the MRS is activated.