Advanced gallium nitride (GaN) technology has become increasingly sought after by space, communication and military agencies around the world. The advantage behind GaN is that it is capable of providing transistors with greater power density capacity at microwave frequencies. GaN power transistors for space applications take up to 5 W/mm through their circuitry. In order to maintain this benefit, packaging technologies need to be equally capable of reducing heat loads (i.e. lowering thermal resistances). The 'Advanced GaN packaging' (Agapac) project developed 25 high-power amplifier packages. These packages are hermetic, thus meeting ESA requirements for air-tight packages. Additionally, up to 65 % added power efficiency was obtained using diamond silver base plate material. To ensure the integrity of these developments, extensive thermal evaluation of these materials was performed. Further testing of the packages were carried out. Conducted at temperatures ranging from – 55 degrees Celsius to 125 degrees Celsius and after 500 cycles no failures were reported. Additional non-destructive tests were performed, such as three-dimensional (3D) X-ray tomography, to reveal any potential voids in the high power amplifier module. Agapac has thus presented space technologies with a viable and commercial packaging that not only enhances Europe's satellite technology, but enables Europe to maintain a strong position in the extremely competitive space industry.