Recent two topics on Schottky barrier at metal/Hf-based dielectric interfaces and atom intermixing at metal/semiconductor interfaces are reviewed. We have constructed a universal theory of Schottky barriers based on a concept of generalized charge neutrality levels. This theory systematically explains barriers of various gate materials, in particular the unusual behavior of p-metals, and naturally reproduces band offsets at various semiconductor/semiconductor interfaces. On the other hand, we have clarified the mechanisms of atom intermixing at various metal/semiconductor interfaces by analyzing the thermal diffusion. It is shown that atom rebonding, screening of bonds, and strain relaxation are important factors to realize the intermixing.