Abstract: A silicon diaphragm piezoresistive pressure sensor having a diaphragm formed by a single-sided fabrication method. The pressure sensor is made up of a substrate on which there is a diaphragm at or near the surface of the substrate with a chamber under the diaphragm. The pressure sensor is fabricated by undercutting a silicon substrate to form a diaphragm and a cavity within the bulk of the substrate under the diaphragm. The fabricating steps including a) forming a buried low resistive layer under a predetermined diaphragm region; b) converting the low resistance layer into porous silicon by anodization of silicon in a concentrated hydrofluoric acid solution; c) removing the porous silicon by selective etching; d) filling the openings formed in the etching of porous silicon with a deposited material to form a sealed reference chamber. Adding appropriate means to the exterior of the diaphragm and substrate to detect changes in pressure between the reference chamber and the surface of the substrate.