Abstract: A 4 GHz~8 GHz wideband high-gain power amplifier based on 0.25 μm gallium nitride high electron mobility transistor technology is presented. The large signal gallium nitride transistor equivalent circuit model is obtained by testing and fitting the S parameters and I-V curve of the model tube, and the large signal equivalent circuit model of GaN tube core is used for accurate simulation design. The power amplifier utilizes two-stage transistor for high-gain design. The input and inter-stage circuits are fabricated by silicon carbide integrated power device process to reduce the matching circuit size. The input synthesis network and the final stage output matching circuit are fabricated by low-loss ceramic. The power amplifier use two 1.2 mm gallium nitride transistors to drive a 12 mm gallium nitride transistor, then combine four 12 mm gallium nitride transistors for 250 W. The measured pulse output power of the power amplifier is great than 250 W in the frequency range of 4 GHz~8 GHz, under the condition of 32 V voltage. The power additional efficiency is great than 38%, and the power gain of the amplifier is great than 18 dB. The power amplifier size is 30.8 mm×27.4 mm×5.0 mm.