A process for fabricating a monocrystalline silicon micromechanical element integrated with a CMOS circuit element within the CMOS technology, wherein a domain of second conducting property is formed within a substrate of first conducting property; the second conducting property is reverse with respect to the first conducting property. A domain of monocrystalline Si is formed within the substrate for fabricating a micromechanical element. A CMOS circuit element as well as a portion of the domain are covered with a protecting layer. Front-side isotropic porous Si-etching from the exposed surface of the domain continues until the portion that will carry the micromechanical element becomes underetched. A porous Si sacrificial layer is created which at least partially encloses the portion. Then the exposed surface of the porous Si sacrificial layer is passivated by applying a metallic thin film thereon. Finally, the metallic thin film that covers the exposed surface of the porous Si sacrificial layer is removed and the porous Si sacrificial layer is dissolved thereby forming the micromechanical element.