High Temperature Pressure Sensors are used in applications where pressure has to be measured at high temperatures. Ordinary pressure sensors cannot operate at such high temperatures. These sensors work on the piezo resistive principle. 
The usual construction is a diaphragm which is filled with oil. The pressure of the media to be measured is thus conducted to the oil. The oil is carried via a capillary tube to the measuring chamber. The temperature of the oil drops in the capillary. The piezo resistive element then measures the pressure of the oil which is the pressure of the media.
Thus the pressure sensor is able to measure pressure at elevated temperature.
Pressure Transducers using the piezo resistive principle can measure pressure at temperatures up to 300 degrees Celsius.
Pressure Sensors designed for operation at very high temperatures use interferometer based sensors.