Polysilazane and silazane-based precursor films were deposited on stacked TiN/Ti/TEOS/Si-substrate by spin-coating, then annealed at 150~400oC, integrated further to form the top electrode and pad, and finally characterized. Theprecursor solutions were composed of 20% perhydro-polysilazane (SiH2NH)n, and 20% hydropolymethyl silazane(SiHCH3NH)n in dibutyl ether. Annealing of the precursor films led to the compositional change of the two chemicals intosilicon (di)oxides, which was confirmed by Fourier transform infrared spectroscopy (FTIR) spectra. It is thought that thedifferent results that were obtained originated from the fact that the two precursors, despite having the same synthetic routeand annealing conditions, had different chemical properties. Electrical measurement indicated that under 0.6MV/cm, a largercapacitance of 2.776×10−11 F and a lower leakage current of 0.4pA were obtained from the polysilazane-based dielectric films,as compared to 9.457×10−12 F and 2.4pA from the silazane-based film, thus producing a higher dielectric constant of 5.48compared to 3.96. FTIR indicated that these superior electrical properties are directly correlated to the amount of Si-O bondsand the improved chemical bonding structures of the spin-on dielectric films, which were derived from a precursor without C.The chemical properties of the precursor films affected both the formation and the electrical properties of the spin-on dielectricfilm.