Pressure sensor cavity etched with hot POCL3 gas

A transmitter in a process control system transmits a pressure over a process control loop. The transmitter includes I/O circuitry, compensation circuitry and an absolute pressure sensor. The I/O circuitry transmits information over the process control loop. Compensation circuitry receives a pressure related signal and responsively controls the I/O circuitry to transmit pressure information on the loop. The absolute pressure sensor includes a cavity which deforms as the sensor deflects in response to an applied pressure. A sensor in the cavity provides the pressure related signal to the compensation circuitry in response to the deformation.