An input buffer circuit for use in a semiconductor device includes a comparator configured to compare a reference voltage with a voltage of an input signal, and output the result of comparison, an activation unit configured to control an activation state of an input buffer in response to an enable signal, a skew adjusting unit configured to change an amount of a current flowing in the comparator in response to one or more skew adjusting signals, and a control signal generator configured to control the enable signal and the skew adjusting signal in response to one or more calibration codes and an input control signal.