A semiconductor device including a data aligner that aligns input data in response to internal strobe signals obtained by dividing a data strobe signal to generate a first alignment data and a second alignment data. The semiconductor device may also include a phase sensor that generates a control clock signal in response to a clock signal and senses phases of the internal strobe signals with the control clock signal to generate a selection signal, and a data selector that selectively outputs the first and second alignment data as a first selection alignment data and a second selection alignment data in response to the selection signal.