Silicon Oxycarbonitride (SiOCN) functionalization is proposed for stable, reproducible, reliable, and enhanced gas-sensing properties in carbon nanotube (CNT) gas sensors. The process is very simple: liquid precursor completely coats the surfaces of the CNTs without requiring any surface modification and a thin layer of semiconductor ceramic SiOCN is created on the CNTs after heat treatment. This new kind of conductometric gas sensors can detect 10ppm NH3 and 2ppm NO2 at temperatures up to 350 degrees C. The stability of the functionalized CNT sensor is verified up to 520 degrees C, while the CNT sensor without the SiOCN coating lost conductance after 250 degrees C due to the structural modification. SiOCN functionalization of CNT changes the recovery from irreversible to reversible and the recovery time decreases from 60min at 100 degrees C to 19min at 350 degrees C.