Rapid thermal oxidations were simultaneously performed on n- and p-type silicon substrates to investigate the saturation currents of metal-oxide-semiconductor (MOS) capacitors. For MOS capacitors on n-type Si substrates, the curves of capacitance versus gate voltage (C-V) show almost no fixed charge, no lateral nonuniformity, and little interface trap density (D-it). The mechanism of the generation of the saturation current is recombination, and was investigated by electroluminescence. Also, the saturation current decreases as the oxide becomes thicker. However, the oxidation temperature must be sufficiently high to form high-quality oxide on p-type Si substrate. Controlled by minority. carrier generation, the saturation current of the MOS (p) capacitor also depends on D-it, suboxide, and bulk trap density. The saturation current increases with the thickness of the oxide. The generation mechanism of the saturation currents of MOS (p) capacitors was also investigated by observing their dependencies on temperature. The mechanisms of the generation saturation currents of MOS capacitors grown on n- and p-type Si substrates are basically different. (c) 2006 American Vacuum Society.