A high efficiency power amplifier includes an integrated circuit with a heterojunction interband tunneling field effect transistor (HITFET) amplifier coupled to receive high frequency (into the GHz) RF signals. The HITFET amplifier is constructed to receive the RF signal with a given frequency at the input terminal and to produce a substantially square wave signal at the given frequency at an output terminal in response to the RF signal applied to the input terminal. The gate of a switching FET connected as a class E amplifier is coupled to the output of the HITFET for receiving the square wave signal and an impedance matching output circuit is coupled to the drain of the switching FET.