An investigation of the influence and role of oxygen in the detection of non-hydrogen containing substances with Pt/SiO₂/SiC based MOS field effect sensors, employing new model systems, has been carried out. With the use of a novel intermediate layer, by which the direct influence of hydrogen on the sensor response can be markedly reduced, the part of the sensor response which is not directly related to hydrogen (which to a small extent is always present in any gas mixture) could be resolved. The Pt/SiO₂ NO reduction/oxidation model system has also been studied from a sensor perspective and the results compared to spectroscopic and mass spectrometry studies of the surface reactions from the field of catalysis. The results support the hypothesis from earlier work that the removal of oxygen from the sensor surface (e.g. by oxidation reactions with CO or NO) to a certain extent directly is involved in the detection of non-hydrogen containing species.