A semiconductor device includes a clock input block to receive a system clock and a data clock, a clock frequency dividing block to generate a plurality of multi-phase data frequency division clocks each of which has the phase difference of a predetermined size by dividing a frequency of the data clock and to determine whether or not phases of the plurality of multi-phase data frequency division clocks are reversed in response to a frequency division control signal, and a first phase detecting block to detect a phase of the system clock based on a phase of a first selected clock that is predetermined among the plurality of multi-phase data frequency division clocks and to determine a logic level of the frequency division control signal in response to the detected result.