In a linear amplifier circuit, an amplifier amplifies an input signal to produce an output signal, an input signal envelope detector detects the envelope of the input signal, and an output signal envelope detector detects the envelope of the output signal. The difference between the outputs of the envelope detectors is determined, and the amplifier is controlled in accordance with the difference so that the level of the output signal is linearly related to the input signal. Compensation circuits are provided for temperature compensation of the linearity in the characteristic of the envelope detectors.