The construction and evaluation of miniature interferometric fibre optic sensors for thermal measurements are described. The sensors are of the Fabry-Perot or Fizeau configuration and comprise a short length of single mode optical fibre with a reflective coating at each end. One end is coated with titanium dioxide, and is fusion spliced to an arbitrary length of similar fibre, which serves to address the sensor, thus facilitating remote operation. The steady state response of the sensors to temperature cycling, and their transient response to pulse heating were investigated. Sensors were constructed with lengths from 0.2 to 20 mm and mean reflectivities ranging from 1% to 25%, leading to visibilities of interference of 0.6 to 0.9. Temperature cycling was carried out from ambient to about 500°C, although operation at temperatures of up to 800°C is considered feasible. The sensors were also demonstrated as heat flux gauges of the calorimetric type.