AbstractIn this paper, a millimeter‐wave broadband high‐efficiency power amplifier (PA) for Ka‐band (26–32 GHz) using 0.15‐μm GaAs pseudomorphic high‐electron‐mobility transistor process is proposed. The PA utilizes a three‐stage cascade structure and adopts an RC series feedback network, which expands the bandwidth and ensures the circuit stability. To improve the output power and efficiency of the circuit, a tree‐like transistor structure is proposed. The power amplifier, it can provide 23.6 dBm output P1dB with 33.1% power‐added efficiency at 28 GHz with high linearity. The maximum small signal gain can reach 27 dB with 3‐dB bandwidth from 24 to 33 GHz for the measured results.