Silicon nitride as a gate dielectric can improve the performance of ULSI CMOS devices by decreasing the gate leakage currents. In this paper we report a a-SiN:H gate dielectric fabricated using Cat-CVD at a relatively low substrate temperature of similar to 250 degreesC, using silane and ammonia as the source gases. The films were deposited at various gas pressures, (NH3/SiH4) flow rate ratios and at different filament temperatures (T-F). The deposition parameters, i.e. total gas pressure and gas composition (silane+ammonia) were optimized to deposit insulating and transparent films with high break-down strength. The structural properties of these films were studied by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. Films with bandgap as high as 5.5 eV were obtained. The optimized conditions were used to deposit ultrathin films of the order of 8 rim thickness for deep-submicron CMOS technology. Electrical properties such as C-V and I-V measurements were studied on metal-nitride-semiconductor (MNS) capacitor structures. These characterization results on MNS capacitors show break-down fields of the order of 10 MV cm(-1) and good interface properties.