A system and method are provided for efficiently amplifying a radio frequency signal. In general, the system includes power amplifier circuitry that efficiently amplifies an input signal under power back-off conditions. In one embodiment, the power amplifier circuitry has an efficiency of at least 30% at a 6 dB back-off point. In addition, DC-DC conversion circuitry operates to control a variable supply voltage provided to the power amplifier circuitry, thereby controlling an output power level, or average output power, of the power amplifier circuitry.