Al2O3 films were grown by metalorganic chemical vapor deposition on p-Si(100) orientation substrates using Al(OC3H7)3 and N2O via pyrolysis. Raman spectroscopy showed the optical phonon modes of the Al2O3/Si structure. The stoichiometry of the Al2O3 film was observed by Auger electron spectroscopy. Capacitance-voltage measurements clearly showed metal-insulator-semiconductor behaviors for the Al/Al2O3/Si diodes with the Al2O3 insulator gate, and the interface state densities at the Al2O3/Si interface were approximately 1011 eV cm-2 at the middle of the Si energy gap. These results indicate that Al2O3 films on Si have potential applications as insulator films.