A semiconductor device, includes a clock delay unit configured to include a plurality of delay units connected in series, where the delay amount of each delay unit varies depending on a level of a control voltage, for delaying a source clock to generate a feedback clock and mixing clocks outputted from the respective delay units to generate a frequency multiplication clock, a harmonic lock determination unit configured to determine whether a harmonic lock has occurred based on a frequency difference between the source clock and the frequency multiplication clock, and a control voltage generator configured to adjust a level of the control voltage based on a phase difference between the source clock and the feedback clock and a determination result of the harmonic lock determination unit.