Abstract: A micromachined pressure switch and method of fabrication from silicon wafers using aligned fusion bonding. Pattern etched thermally grown silicon dioxide insulating pads are used to determine the size of silicon pressure membranes on an upper silicon wafer, with the desired switch gap set by the oxide thickness. The silicon membranes are formed by controlled thinning the upper silicon wafers. V-shaped vent grooves are pattern etched into a bottom silicon wafer to form electrodes to which the insulating pads are fusion bonded. The area between the electrodes and the membrane forms wells of specified sizes into which the membranes deflect upon application of pressure. The pressure switch operates when the membrane is deflected to contact the electrodes in the bottom wafer, and closes at the desired pressure threshold for both directions of pressure change with negligible hysteresis. The method of fabrication applies to a single element pressure switch as well as to an array of pressure switches.