A power amplifier circuit includes a power supply module and serially connected multi-stages of amplifier circuit. The multi-stages of amplifier circuit, coupled to the power supply module for amplifying an radio frequency (RF) input signal as an RF output signal, which include a driver stage of circuit and a gain stage of circuit. The driver stage of circuit receives and amplifies the RF input signal. The driver stage of circuit is powered by a first supply voltage received from the power supply module. The gain stage of circuit amplifies the signal received from previous stage of amplifier circuit and outputs the RF output signal. The gain stage of circuit is powered by a second supply voltage received from the power supply module. When the power amplifier circuit is operated in a back-off region, the first supply voltage is lower than the second supply voltage.