A semiconductor memory device may include a control signal generation circuit, a period signal generation circuit and a selection circuit. The control signal generation circuit may be configured to generate a control signal in response to a mode signal, a voltage detection signal and a temperature detection signal. The period signal generation circuit may be configured to generate a period signal periodically transited in response to the control signal. The selection circuit may be configured to output, in response to the control signal, any one of the period signal and a signal from an external device that is buffered.