A semiconductor device includes an initial buffer signal generation circuit and a buffer signal generation circuit. The initial buffer signal generation circuit includes an initial buffer circuit which is activated if an initialization operation terminates. The initial buffer signal generation circuit generates an initial buffer signal from an external control signal in response to a first reference voltage signal. The buffer signal generation circuit includes a buffer circuit which is activated in response to the initial buffer signal. The buffer signal generation circuit generates a buffer signal from the external control signal in response to a second reference voltage signal.