Based on the 0.25 μm GaN technology and High Electron Mobility Transistor(HEMT) on SiC substrate, a high power, high gain and high efficiency C-band broadband Monolithic Microwave Integrated Circuit(MMIC) amplifier is developed. The gain and the output power index of the circuit are guaranteed by means of reactance matching, optimizing the static DC working point of the circuit, and selecting the gate width ratio of the three-stage amplifier 1:3.6:16. The test results show that the chip in 4–8 GHz frequency range, the drain voltage 28 V, under continuous wave condition, the small signal gain of the MMIC is greater than 30 dB, the large signal gain is greater than 23 dB, the saturation output power is greater than 44 dBm, the power added efficiency is 38% to 45%. The size of the MMIC is 3.6 mm×4 mm.