The experimental characterization of an innovative optical system for detection of carbon monoxide (CO) is reported. In this system a photodetector based on gallium nitride (GaN) and an UV light source are integrated. The gas flows between the light source and the GaN photodetector. The UV light source consists of a spark produced by an arc discharge which induced transitions in the gas, causing a modification of the light intensity as a function of gas composition. These transitions modify the fraction of light in the UV spectral region which is detected by the GaN-photodetector, as a function of the species concentration. By virtue of its structural properties, gallium nitride (GaN) allows to operate at high temperature and high speed and to work in-situ in the exhaust manifold of combustion engines at temperatures as high as 600degC, at which the deposited organic residuals on the detector can be oxidized. This …