A semiconductor device includes a clock delay section configured to receive an external clock signal, reflect different delay amounts on the external clock signal, and generate a plurality of synchronization clock signals, a clock synchronization section configured to synchronize a clock enable signal with each of the plurality of synchronization clock signals in an order beginning with a synchronization clock signal, on which a largest delay amount is reflected, to a synchronization clock signal, on which a smallest delay amount is reflected, and to generate a synchronized clock enable signal, and an internal clock generation section configured to generate an internal clock signal corresponding to the external clock signal, and to be on/off controlled in its operation in response to the synchronized clock enable signal.