Abstract: Monolithic microwave integrated circuit (MMIC) components and micro electromechanical systems (MEMS) components are integrated onto a single substrate at a wafer scale, by first performing MMIC and MEMS fabrication on a front face of a thick substrate wafer, bonding the substrate wafer to a cover wafer, thinning the back face of the substrate wafer and, finally, completing MMIC and MEMS fabrication on the back face of the thinned substrate wafer. The fabrication process is facilitated by use of a guard ring between the wafers to provide additional mechanical support to the substrate wafer and to protect the devices while the MMIC/MEMS fabrication is completed, and by a low temperature bonding process to join the substrate wafer and the cover wafer at multiple device cavity seal rings.