NOVELTY - The semiconductor device comprises a semiconductor substrate (108), a semiconductor mass element (112) to move in response to an applied acceleration, a capacitive sensing element to sense movement of the mass element, a complementary metal-oxide-semiconductor (CMOS) circuit formed on the substrate, and a capping layer contacting the substrate and capping the mass element. The mass element is defined by trenches etched into the semiconductor substrate and a cavity (110) below the mass element. The sensing element comprises a doped sidewall and top of the mass element.    USE - The semiconductor device is useful as an acceleration sensor of an application specific integrated circuit system, which is useful in a component of an automobile and battery powered device (all claimed) to detect a movement of a portable electronic device for managing battery power, where the system is portable electronic device, and the automobile component is an airbag or tire.    ADVANTAGE - The semiconductor device is compact, can be economically manufactured with high reliability, and provides high degree of freedom in structuring the oscillating mass element.    DETAILED DESCRIPTION - The semiconductor device comprises a semiconductor substrate (108), a semiconductor mass element (112) to move in response to an applied acceleration, a capacitive sensing element to sense movement of the mass element, a complementary metal-oxide-semiconductor (CMOS) circuit formed on the substrate, and a capping layer contacting the substrate and capping the mass element. The mass element is defined by trenches etched into the semiconductor substrate and a cavity (110) below the mass element. The sensing element comprises a doped sidewall and top of the mass element, a doped sidewall of the substrate opposite to the doped sidewall of the mass element and a doped portion of the capping layer. The capping layer is separated from the mass element by a gap. A top of the capping layer is coplanar with a top of the substrate. The mass element is connected to the substrate via a semiconductor material portion between a sidewall of the mass element and sidewall of the substrate and between a bottom of the mass element and a bottom of the cavity. INDEPENDENT CLAIMS are included for:    (1) a system such as portable electronic device; and    (2) a method for fabricating a semiconductor device.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of an acceleration sensor.    Acceleration sensor (106a)    Substrate (108)    Cavity (110)    Mass element (112)    Cap. (114)