A semiconductor chip includes a write clock buffer, a voltage regulator, a process calibration circuit and a temperature calibration circuit. The voltage regulator generates plural regulated voltages. The process calibration circuit output one of the regulated voltages as a bias voltage of the write clock buffer, depending on a process variation of the semiconductor chip. The temperature calibration circuit track a temperature variation of the semiconductor chip in real time, performs analog calibration on the bias voltage from the process calibration circuit in real time depending on a result of the tracking, and outputs the analog-calibrated bias voltage to the write clock buffer.