A system on chip (SOC) is provided. The SOC includes a system core logic, a voltage regulator, a clock generator and a system balance circuit. The voltage regulator provides an operating voltage to the system core logic and receives a current setting signal to set the voltage regulator to a low current mode or a high current mode. The clock generator provides a reference clock signal. The system balance circuit receives the reference clock signal to provide the current setting signal to the voltage regulator and provides the system clock signal to the system core logic, wherein the current setting signal is used to set the voltage regulator to the high current mode before the system clock signal is enabled, and set the voltage regulator to the low current mode after the system clock signal is enabled.