An internal voltage generator of a semiconductor memory device generates an internal voltage sensitive to a change in a temperature. The internal voltage generator includes a reference voltage generator, an internal voltage detecting unit and an internal voltage pumping unit. The reference voltage generator generates a reference voltage which is inversely proportional to the change in the temperature. The internal voltage detecting unit detects a difference between the reference voltage and the internal voltage to output a pumping control signal according to a detecting result, wherein the pumping control signal has an identical temperature characteristic as the reference voltage. The internal voltage pumping unit generates the internal voltage by a pumping operation in response to the pumping control signal.