A micromechnical sensor having a polysilicon beam that is an integral part of the diaphragm resulting in a frequency of the beam that is a direct result of the pressure applied to the external surface of the diaphragm. Fabrication of this resonant microbeam sensor has no backside wafer processing, and involves a process and layout independent of wafer thickness for high yield and robustness. Both the diaphragm and resonant beam are formed from polysilicon. The sensor may have more than one resonant beam. The sensor beam or beams may be driven and sensed by electrical or optical mechanisms. For stress isolation, the sensor may be situated on a cantilevered single crystal silicon paddle. The sensor may be recessed on the isolating die for non-interfering interfacing with optical or electrical devices. The sensor die may be circular for ease in mounting with fiber optic components.