In this paper a new method of depositing silicon nitrided oxide by an in-situ process is introduced. Thin nitrided-oxide (NO) films were deposited on silicon by rapid thermal oxidation and rapid thermal chemical vapour deposition (RTCVD). Thin oxide films, 10.0 nm, were rapidly thermally grown in a dry oxygen ambient at 1000-degrees-C and the silicon-nitride films were deposited on the oxide at 700-900-degrees-C using an NH3 and SiH4 gaseous mixture. The effect of the NH3/SiH4 input ratio and the deposition temperature on the deposition rate and the electrical properties was studied. The experimental results show that the deposition rate increased with increasing deposition temperature and decreasing NH3/SiH4 input ratio. From the data for the Fourier-transform infrared spectroscopy (FTIR) and the C-V curves of the NO films, it was observed that the flat-band voltage is directly related to the N-H-bond peak intensity. The flat-band voltage shifts to the positive with increasing deposition temperature and to the negative with increasing NH3/SiH4 input ratio, and the breakdown field of NO films is higher than that of the RTP oxidation (RTO) films.