Interfacial reactions of the Pt-Ti-Si structures were studied in this work. The rule of the Ti interlayer is to react with native oxide on the Si substrate and form the Ti-O solid solution or titanium oxide depending on the Ti-layer thickness; A Ti-oxide layer between Pt and Si was found when the Ti-layer thickness was less than 5 nm. This layer acted as a diffusion barrier and inhibited the reactions between Pt and Si. For the Ti-layer thickness above 5 nm. the Ti-O solid solution was formed instead. Auger depth profiles showed that the Ti-O layer moved outward as the silicidation process proceeded. An improvement in the smoothness of the PtSi-Si interface was obtained.