A Ka-band Doherty power amplifier (PA) is presented in this paper. The proposed Doherty PA is designed using 0.15-μm GaAs enhancement-mode pHEMT process to achieve an output saturation power up to 25.1 dBm. The quarter-wave transmission lines and offset lines are implemented using inductance-capacitance lumped elements to reduce significantly the chip area. With a compact chip size of 1.5×1.5 mm2, the measured small signal gain, input and output return losses at 25.8 GHz are better than 7 dB, 15 dB, and 29 dB, respectively. The proposed Doherty PA achieves a peak power-added efficiency of 16.5% and a 6-dB back-off efficiency of 12.6%. This work has potential for the high-power high-efficiency communication system as compared to previously reported Doherty PAs.