Behavior of Fe impurity at the Si-SiO2 interface of a metal-oxide-semiconductor (MOS) made through HCl oxidation was studied with electrical measurements and transmission electron microscopy. Fe impurity was introduced in silicon wafers by ion implantation to the doses of 1.0 x 10(15) and 1.0 x 10(14) cm(-2). The wafers were then oxidized in HCl/O-2 ambient. The Fe impurity either nucleated (1.0 x 10(15) cm(-2)) to precipitates in the Si substrate near the Si-SiO2 interface or scattered uniformly in the SiO2 (1.0 x 10(15) and 1.0 x 10(14) cm (-2)). The precipitates were identified as metallic alpha-FeSi2 or semimetallic FeSi. The precipitate is supposed to form a weak spot in the silicon oxide, where the electric field is strengthened; however the dielectric effect of uniformly scattered Fe impurity in the SiO2 film is relatively small. Fe precipitates were gradually included into the SiO2 film and finally dissolved during HCl oxidation. As a result, Fe impurity was scattered in the middle area of the SiO2 film. The gettering ability of HCl oxidation is attributed to its enhancement of dissolution of Fe-silicides in the SiO2 film.