Abstract: A power amplifier with high reliability and high PAE (power added efficiency) is designed and realized within X-band, i. e. , from 8.0 GHz to 8.5 GHz, by means of the internal matching technology and two GaN HEMT transistors. Based on the transistor and load-pull data provided by the Nanjing Electronic Devices Institute, the input and output impedances of the transistor are all matched to 50 Ω by utilizing the "L-C-L" matching network and Wilkinson power divider/combiner. By using two transistors, under the working state of -2.2 V grid voltage, 24 V drain voltage and continuous wave, the output power is greater than 20 W and the power gain is greater than 10 dB within the target frequency band. Besides, for the proposed power amplifier the overall PAE is better than 49.7%, where over 52% PAE has been achieved from 8.1 GHz to 8.4 GHz. This performance is better than the current PAE of the matching power amplifier at the similar frequency band in China. Finally, the reliability of the power amplifier has been successfully verified by experiments.