A skew calibration circuit may include a data delay unit receiving first data and a first code, and output delayed first data as second data by delaying the first data according to the first code; a clock delay unit receiving a first clock signal and a second code, and output delayed first clock signal as second clock signal by delaying the first clock signal according to the second code; a multiplexer receiving a clock signal and output the clock signal or an inverted clock signal of the clock signal as a first clock signal in response to a selection signal; and a control logic unit receiving the second data and the second clock signal and control the first code, the second code and the selection signal in response to the second data and the second clock signal.