We report on an all-optical sensor system that employs InGaN/GaN nanowires (NWs) as opto-chemical transducers. The NWs, grown by plasma-assisted molecular beam epitaxy on low-resistivity n-type Si (1 1 1) substrates, exhibit an efficient room-temperature photoluminescence (PL) that persists up to about 200 °C. After deposition of a thin (5 nm) catalytic Pt-film onto the NWs the PL intensity rises when the NWs are exposed to small concentrations of hydrogen and hydrocarbons. The gas response of the NWs was analyzed using an integrated sensor system with fiber-coupled excitation from a GaN-based power LED emitting at 365 nm and a fiber coupled photo multiplier tube for detection. With this setup, H2 concentrations as low as 200 ppb and C2H2 concentrations as low as 5 ppm could be detected when the transducers were operated at temperatures around 80 °C. This opto-chemical transducer principle is best suited for safety-critical applications where a reliable media separation is required.