Microstructures and interdiffusions of Pt/Ti/SiO2/Si and RuO2/SiO2/Si during annealing in O2 were investigated using x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The degree of oxidation and the interdiffusion of elements have remarkably increased with increasing temperature above 500 °C for the Pt/Ti/SiO2/Si case. The generation of Pt hillocks commenced at 500 °C. The Pt-silicide phase was also observed near the TiOx/SiO2 interface. The microstructural variations occurred to only a small amount for the RuO2/SiO2/Si case over the temperature range 300 – 700 °C. While there was no hillock formation, the RuO2 film surface was roughened by the thermal grooving phenomenon. A thin interlayer phase was found at the RuO2/SiO2 interface.