Carbon-nitride films with -20 nm grain size have been deposited on silicon substrate for applying to integrated humidity sensors. Crystal structure, surface morphology and bonding structures of the deposited films were investigated by XRD, SEM and FTIR. Carbon nitride films have hydrogen defect, this offer the adsorption sites to water molecules. An integrated humidity FET that was fabricated by 0.8 microm CMOS technology was sensitive to humidity changes. A gas adsorption model was proposed in gas-carbon nitride interface.