This paper presents a high power amplifier at K-band (20.2 - 21.2 GHz). The AlGaN/GaN CPW MMIC amplifier is realized with 0.25 mu m HEMT process on 2-inch semi-insulating SiC substrate. The amplifier has a small signal gain over 20 dB for Vds=15V and measured output power of over 31 dBm at 20.2 Ghz. PAE of the amplifier is around 22% for desired frequency band. Initial radiation hardness tests indicate a suitable stability of the technology in space.