A Doherty amplifier has a distributor for branching an input signal into two signals, a carrier amplifier to which one of the signals is inputted from the distributor, a peak amplifier to which another signal of the signals is inputted from the distributor, and a synthesizer for synthesizing output signals from the carrier amplifier and the peak amplifier. The carrier amplifier has a compound semiconductor device with at least two terminals. The peak amplifier has a single element semiconductor device. Bias voltages having the same polarity are applied to the two terminals of the compound semiconductor device.