The present invention relates to integrating an inertial mechanical device on top of an IC substrate monolithically using IC-foundry compatible processes. The IC substrate is completed first using standard IC processes. A thick silicon layer is added on top of the IC substrate. A subsequent patterning step defines a mechanical structure for inertial sensing. Finally, the mechanical device is encapsulated by a thick insulating layer at the wafer level. Compared with the incumbent bulk or surface micromachined MEMS inertial sensors, vertically monolithically integrated inertial sensors provided by embodiments of the present invention have one or more of the following advantages: smaller chip size, lower parasitics, higher sensitivity, lower power, and lower cost.