there is disclosed , for use in an rf amplifier , a biasing circuit for maintaining the quiescent current of an output power transistor at a selected bias level . the biasing circuit comprises a temperature sensor circuit for generating a temperature - sensitive control voltage that varies according to changes in temperature of the output power transistor and a bias voltage generating circuit capable of detecting a variation in the temperature - sensitive control voltage . in response to a detected change in the temperature - sensitive control voltage , the bias circuit adjusts a bias voltage applied to the output power transistor by an amount suitable to offset a change in the selected bias current level caused by a temperature change related to the variation in the temperature - sensitive voltage .