A semiconductor device includes a reset signal generator configured to change the number of activated signals among a plurality of reset signals according to a frequency of an external clock, a plurality of mixing control signal generators configured to generate a plurality of first and second mixing control signals, and a clock mixer configured to generate a mixing clock by mixing a first driving clock and a second driving clock, wherein the first driving clock is generated by driving a positive clock of the external clock according to the plurality of first mixing control signals, and the second driving clock is generated by driving a negative clock of the external clock according to the plurality of second mixing control signals.