Abstract: In this paper, an X~Ku band broadband 1 W driver amplifier MMIC based on 0.25 μm GaN HEMT on SiC process is designed. The design uses an equivalent RC model of active devices' large-signal output impedance for verifying the accuracy of the GaN HEMT process model. And large-signal output impedances of GaN HEMT with different dimensions are achieved. Negative feedback structure is applied for the first-stage transistor to reduce the Q value of the matching network. The broadband matching is successfully achieved through band-pass matching network topology. The measurement results show that this driver amplifier at 28 V operation voltage achieved over 30 dBm output power, 21% power added efficiency and 15 dB power gain from 8 GHz to 18 GHz. The chip size is 2.20 mm×1.45 mm. The MMIC chip has the characteristics of wide bandwidth, high efficiency and small size. It can be mainly used in fields such as millimeter-wave transceiver components and wireless communication, and has broad application prospect.