Quasi-monolithic integration combines hybrid and monolithic integration of passive and active (high-frequency) devices. High power chip transistors (based on gallium nitride) for high-frequency applications are embedded in cost effective silicon substrate (bulk micromachining) and planar electrical contacts are fabricated using thin film technology (surface micromachining). Subsequently passive devices (resistors, inductors, capacitors) can be fabricated using thin film technology so that complete circuits on cost effective silicon substrate as carrier material are possible.