This paper reviews some of our recent work on the surface modification of silicon related materials by applying gas-decomposition reactions in a catalytic chemical vapor deposition (Cat-CVD) system. In the case of oxidation of Si, ultra-thin SiO2, films are formed at temperatures as low as 240 degreesC. The electrical properties and the dielectric constant are comparable to those of conventional thermally oxidized films. In the case of nitridation of SiO2, the surface Of SiO2/Si(100) is nitrided at temperatures as low as 200 degreesC and X-ray photoelectron spectroscopy (XPS) measurements revealed that incorporated N atoms are bound to Si atoms and O atoms and located at the top-surface of SiO2.