A semiconductor device includes an output controller and a data strobe signal generator. The output controller generates a period signal and a control clock signal according to a read operation signal generated to execute a read operation, an internal clock signal generated in synchronization with a clock signal, and an expansion control signal. The data strobe signal generator generates a data strobe signal according to the control clock signal during a period that the period signal is enabled. The period that the period signal is enabled expands according to the expansion control signal.