PURPOSE: To reduce the loss of power amplifier and to improve the linearity through the application of temperature compensation by adding a voltage corresponding to a threshold voltage of a power device of the power amplifier to an input signal to form a drive signal.

CONSTITUTION: An input signal VIN is outputted to an adder circuit 3 as a voltage VTH corresponding to the threshold voltage VTH of the power amplifier circuit 1 by a threshold voltage generating circuit. The circuit 3 adds an output VF of a negative feedback circuit 4, the input signal VIN and the output VTH of the circuit 2 and outputs a drive voltage VDR to the amplifier circuit 1. The amplifier circuit 1 amplifies only the threshold voltage VTH or over of a power MOS FET in the voltage VDR and outputs the result to a load 5 as a transmission output voltage VOUT. The voltage VOUT enters the negative feedback circuit 4, where a negative feedback voltage VF is formed. A drain loss takes place only when the signal VIN is given and since negative feedback is applied even with the voltage VTH of the power MOSFET varied with temperature, no temperature compensation is required.