This concise volume examines the characteristic electronic parameters of semiconductor interfaces, namely the barrier heights of metal-semiconductor or Schottky contacts and the valence-band discontinuities of semiconductor-semiconductor interfaces or heterostructures. Both are determined by the same concept, namely the wave-function tails of electron states overlapping a semiconductor band gap directly at the interface. These interface-induced gap states (IFIGS) result from the complex band structure of the corresponding semiconductor. The IFIGS are characterized by two parameters, namely by their branch point, at which their charge character changes from predominantly valence-band- to conduction-band-like, and secondly by the proportionality factor or slope parameter of the corresponding electric-dipole term, which varies in proportion to the difference in the electronegativities of the two solids forming the interface. This IFIGS-and-electronegativity concept consistently and quantitatively explains the experimentally observed barrier heights of Schottky contacts as well as the valence-band offsets of heterostructures. Insulators are treated as wide band-gap semiconductors. In addition, this book: Explains intrinsic interface states of electron states that overlap the band gap of a semiconductor at the interface Includes experimental data on Schottky contacts including carrier height, ideality factor and flat-band barrier height Compares of Theoretical and Experimental Data for a range of semiconductors.