We have successfully grown ultrathin oxides on large area of silicon wafers by the microwave plasma afterglow oxidation method. Analysis of the Fourier transform infrared spectra indicates that the general bonding structures of the ultrathin oxides grown by microwave plasma afterglow oxidation at 700 degrees C could be identical to those grown by dry O-2 thermal oxidation. Electrical property measurements (e.g., time-zero dielectric breakdown and time-dependent dielectric breakdown) are also investigated. Based on our results, we conclude that microwave plasma afterglow oxidation is a useful method for the preparation of large area ultrathin oxide films on silicon substrates.