Since the Turbine Inlet Temperature (TIT) is a critical parameter for the optimization of Gas Turbine working conditions, an innovative temperature sensor, based on spectroscopic photometric measurements of the infrared radiation emitted in a selected wavelength band by the CO2 molecules present in the combustion gases is proposed. The measured quantity is the grey body spectral irradiance H (λ,T) defined by the product of the blackbody spectral irradiance WB (λ,T) and the grey body absorption Abs (λ,T), the blackbody spectral irradiance being defined by the well known Planck’s law. To achieve a black body condition, irradiance measurements have to be carried out in a very narrow spectral range (about 15 nm wide, around 4 microns) where the carbon dioxide molecules strongly absorb the IR radiation. In this way the detected signal is proportional to the gas temperature and follows its temporal behavior. Unfortunately, since the measured signal depends on geometrical and optical parameters that can hardly be theoretically evaluated, it turns out that it is very difficult to get the absolute temperature in the absence of an external independent reference measurement, to overcome this problem we have implemented an innovative method. The validity of the proposed method has been checked by means of laboratory tests carried out under controlled temperature conditions.