Abstract: A sensor system and method for a power electronics module is discussed. The system comprises a optical fibre 318 mounted inside the module housing 302 and connected to an external sensor system 320 (not shown). The optical fibre 318 is arranged so that it lies proximate to one or more semiconductor dies 308 within the housing, and can sense their temperature. The fibre can be connected to the die 308 by glue, mechanical connection, or can in other examples by provided in the underlying support structure such as a DCB (direct copper bonded ceramic structure) or base plate 304. The fibre can contain an optical grating, such as an FBG or LPG, or can operate based on interferometry, to detect temperature or strain.