We present a detailed microscopic investigation of interactions and reactions occurring at refractory-metal silicon interfaces at room temperature. High resolution core level photoemission results for Ti coverages in the range 0.2–16 monolayers on cleaved Si(111)2×1 show that three new distinct Si environments are created by semiconductor surface disruption. In agreement with heats of formation or electronegativity differences, all the chemical shifts are at lower binding energy. Each of them represents a different metal-Si coordination or configuration. Analogous results for Sc overlayers indicate that at least two reacted species are present. For both Ti and Sc, the reaction is started at submonolayer coverages. Analysis of the Si 2p intensity attenuation curves shows an evolution characterized by the sequential growth of the different species. Indeed, each species grows, reaches saturation, and is then attenuated. This is associated with the competition between diffusion and reaction at the interface.