Abstract: Fabrication of semiconductor devices with movable structures includes local oxidation of a wafer and oxide removal to form a depression in an elevated bonding surface. A second wafer is fusion bonded to the elevated bonding surface and shaped to form a flexible membrane. An alternative fabrication technique forms a spacer having a depression on a first wafer and active regions on a second wafer, and fusion bonds the wafers together with the depression over the active regions. Devices formed are integrable with standard MOS devices and include FETs, capacitors, and sensors with movable membranes. An FET sensor has gate and drain coupled together and a drain-source voltage which depends on the gate's deflection. Selected operating current, channel length, and channel width provide a drain-source voltage linearly related to gate deflection.