An optical pressure sensor has been designed using silicon micromachining technology. A resonant silicon beam is mounted above a diaphragm and its resonant frequency changes with applied pressure. The sensor is temperature compensated by way of a second pressure-insensitive resonator. Both resonators are optically addressed via the same optical fiber. The sensor is designed to give an overall accuracy of 0.05% full-scale pressure, which is currently between 130 kPa or 3 MPa. Optical technology allows the optical pressure sensor to operate in a harsh aerospace environment where electronic pressure sensors cannot survive.