The transition metal–silicon interface is highly reactive; the reactivity induces material reactions altering the stoichiometry, atomic structure, and chemical bonding at the interface. For such an interface, it is essential to study the interfacial reaction and chemistry in order to understand the formation of Schottky barriers. This paper first reviews the present knowledge on the electronic and microstructural characteristics of the transition metal–silicon interface. The discussion focuses on the extent of atomistic details regarding these interface properties that can be extracted from existing results. This is followed by a summary of barrier height data obtained from two types of measurements. One, with thick-film (∼100 Å) coverages, demonstrates that the barrier height of a well-reacted silicide overlayer is large unaffected by changes of the material characteristics of the silicide phase. And the other, with a few monolayers of metal coverage, reveals that the barrier can be established with a few Å of metal coverage. These experiments establish the true interfacial character of the barrier height. Based on the extent of interfacial reaction, the nature of the transition metal–silicon interface can be classified to be extrinsic or intrinsic. The extrinsic interface contains various defects from processing and surface preparation, which control to a significant extent its barrier height. As the reaction proceeds to complete silicide formation, an intrinsic interface is formed where the barrier height seems to be determined primary by chemical bonding originating from metal–silicon interaction at the interface.