The main objective of the Covered Gallium Nitride (CoGaN) project is the demonstration of the electrical performance of a GaN HPA in a frequency range between 25 GHz and 40 GHz with a maximal output power of 5 W in a chip scale packaging technology for 5G applications. In addition, requirements are existing for reliability testing at THB condition of 85°C/85% rel. humidity. In this work a test vehicle circuit with a pre matched 1 mm transistor is used for showing the process feasibility.