In one embodiment, the process flow for a capacitive pressures sensor is combined with the process flow for an inertial sensor. In this way, an inertial sensor is realized within the membrane layer of the pressure sensor. The device layer is simultaneously used as z-axis electrode for out-of-plane sensing in the inertial sensor, and/or as the wiring layer for the inertial sensor. The membrane layer (or cap layer) of the pressure sensor process flow is used to define the inertial sensor sensing structures. Insulating nitride plugs in the membrane layer are used to electrically decouple the various sensing structures for a multi-axis inertial sensor, allowing for fully differential sensing.