Buried SiO2 layers were formed by oxygen-ion(16O+) implantation into silicon. The impurity distribution of the oxygen-implanted silicon substrate was analyzed by Auger spectroscopy. The properties of the buried SiO2 layers were investigated by infrared spectra, C-V characteristics, dielectric strength, dielectric constants, and refractive indices. The epitaxially-grown silicon layer on the buried SiO2 layer showed a good monocrystalline state. MOS devices were fabricated using the epitaxial silicon layer, and the field effect mobilities of holes and electrons were 240 and 610 cm2/V· s, respectively, for 5 V gate bias. 21-stage C-MOS ring oscillators with effective channel length of 3.1 µm were fabricated. The propagation delay time and the dissipation power were 0.83 ns/stage and 0.33 mW/stage, respectively, for 5 V operation of the oscillators.