An internally matched power amplifier including an input terminal for receiving an input signal and an output terminal; a plurality of semiconductor devices connected with the load electrodes in series; transmission means for coupling the load electrodes of neighboring devices in the series and establishing an internal impedance match; the last device in the series having its other electrode connected to the output terminal; the first device in the series having its control electrode connected to the input terminal and its other load electrode connected to a common conductor and having a predetermined d.c. bias level and a predetermined signal voltage level between its control and its other electrode; first means for setting the control means of each device but the first in the series to the predetermined signal voltage level and second means for biasing the control electrode of each device but the first in the series to the predetermined d.c. bias level.