A novel cadmium and germanium oxynitride (CdGeON) sensor, originally designed for NH3 and SK2 detection, has been studied by in situ Fourier transform diffuse reflectance infrared spectroscopy (DRIFTS), XPS, and UV-vis in order to elucidate the influence of an oxygen-containing environment on the sensor’s electrical response. Under oxygen, the conductivity of this sensor is directly related with DRIFTS bands at 810, 780, and 580 cm(-1) assigned to oxygenated species bonded to single Ge atoms. These species are reversibly eliminated or restored in the solid framework upon heating in N-2 Or synthetic air, respectively. XPS and UV-vis spectroscopies have confirmed the oxygen uptake and the increase in the coordination number of Ge atoms upon exposure of the CdGeON sensor to synthetic air. A similar conclusion is presumed for Cd atoms although no conclusive results can be inferred from the W-vis spectra. From the analysis of the resistance-temperature Arrhenius-type relationships, a model involving the filling of anionic vacancies is proposed to explain such a differenciated behavior under synthetic air.