A multi-stage RF/Microwave power amplifier circuit is provided that is capable of operating efficiently at multiple output power levels. The amplifier comprises first and second amplifying stages, an output impedance matching network connected to the output of first amplifying stage and an interstage impedance matching network connected between the outputs of said first and second amplifying stages. In a high power mode, the first amplifying stage is enabled and the second amplifying stage is disabled and the output and interstage impedance matching networks present a first value of the output impedance that improves the efficiency of the first amplifying stage. In a low power mode, the first amplifying stage is disabled and the second amplifying stage is enabled, and output and interstage impedance matching networks present a second value of the output impedance that improves the efficiency of the second amplifying stage.