A two stage power amplifier circuit that employs both a DC to DC converter and sliding bias controller to improve power amplifier efficiency. The control signal that is generated by the power detector circuit to control the input voltage to the DC to DC converter is also used to provide the reference voltage that controls the sliding bias controller. The sliding bias controller reduces the quiescent current of the power amplifiers by reducing the bias currents, and thus the DC voltage at lower power output levels driving the power amplifiers. This causes the power amplifiers to operate at or near higher efficiency Class B operation at lower power output levels. As the power level increases, the sliding bias controller reduces its control on the bias currents so that the power amplifier can be driven at necessary higher power output levels.