Si SiO 2 interface states within the conduction band of Si have been examined using Al-gate metal-oxide-semiconductor (MOS) capacitors with very thin oxide films, 2.5–3.0 nm thick, thermally oxidized in dry O 2. We have developed methods of observation and calculation on the interface states by measuring the direct tunneling current through the oxide. It has been found from this method that there exist interface states within the conduction band and that their density distribution has two sharp peaks located at 7±1 and 17±1 meV above the conduction band edge. Both the peak energies are independent of the oxidation temperature, and the total state density at the interface as-oxidized at 850°C is larger than that at 1000°C.