An etching monitoring apparatus and related method for use in the manufacture of microstructures (and in particular MEMS) located within an etching chamber is described. The apparatus and related method operates by setting the temperature of the chamber within which the microstructure is located at a starting temperature, and maintaining the partial pressure of an etching gas within the chamber at a constant value. As a result the surface temperature of the micro structure within the chamber is primarily determined by the etch rate. Therefore, by employing a thermometer to monitor the change in etching surface temperature, a direct diagnostic for monitoring the etching process is provided.