An X-band gallium-nitride high electron mobility transistor (GaN HEMT) transformer-based Doherty power amplifier (TBD PA) module with a phase lineariser has been developed. The TBD PA uses Cree's 6 W GaN HEMT bare die and realised in seven-layer PCB. The proposed lineariser is employed before the TBD PA to compensate the phase distortion during the Doherty operation. The implemented TBD PA with 9.56 GHz continuous wave test shows a 38.5% power-added efficiency at 39.6 dBm output power. Linearity characterisation is also performed using 40 MHz bandwidth, two carriers aggregated long-term evolution-advanced signal and shows −35.4 dBc carrier aggregation evolved-universal terrestrial radio access adjacent channel leakage power ratio which is 7 dB enhanced after phase compensation.