Abstract: Distributed amplifier is an amplification structure which can realize ultra-broadband amplification. However, due to the output power density of transistors,distributed amplifier was found application mostly in small signal amplification. The third generation wide band gap semiconductor GaN present itself with the characteristics of high breakdown voltage and high output power density. By applying GaN technology to distributed amplifier, a wideband power amplifier can be dem onstrated. We design a 0. 3 ~2. 5GHz multi octave distributed power amplifier with four GaN HEMTs(High Electron Mobility Transistor) and realize it with HMC(Hybrid Monolithic Circuit) technology. The measure result shows that the saturated output power is above 39dBm and PAE is larger than 15% in the 0. 3 ~2. 5GHz bandwidth with a linear above 8dB.