A semiconductor memory device performs a refresh operation stably even while a temperature continuously changes at near a specific temperature. The semiconductor memory device includes an on die thermal sensor (ODTS) and a control signal generator. The on die thermal sensor (ODTS) outputs a thermal code corresponding to a temperature of the semiconductor memory device. The control signal generator generates a self refresh control signal in response to the thermal code, wherein a state of the self refresh control signal does not change when the temperature variation is less than a predetermined value.