Currently, the solution for the problem of temperature measurement of the gas phase of combustion products inside the combustion chambers of gas turbine engines is still in progress. Conventional thermocouples, which are the industry standard, are intrusive and provide spatially and temporally averaged data. In this work, a spectral system for the temperature measurement of gas flow inside the combustion chamber has been developed. The system is based on the method of multi-wave pyrometry of soot in the visible optical range and comprises a multispectral sensor-on-chip solution. Field tests on the gas turbine engine confirmed that the presented system allows measuring temperature in the range from 810 to 1120 °C with a measurement error of 3%.