A Doherty power amplifier circuit having a main power amplification device, an auxiliary power amplification device arranged in parallel with the main power amplification device, and a load modulation circuit comprising a harmonic injection circuit connected with respective outputs of the main power amplification device and the auxiliary power amplification device. The harmonic injection circuit is arranged to transfer harmonic components generated at the main power amplification device to the auxiliary power amplification device and harmonic components generated at the auxiliary power amplification device to the main power amplification device, when both the main and auxiliary power amplification devices are operating, for modulating the respective outputs of the main power amplification device and the auxiliary power amplification device.