Almost all semiconductor devices contain metal-semiconductor, insulator-semiconductor, insulator-metal and/or semiconductor-semiconductor interfaces; and their electronic properties determine the device characteristics. This is the first monograph that treats the electronic properties of all different types of semiconductor interfaces. Using the continuum of interface-induced gap states (IFIGS) as a unifying theme, Mnch explains the band-structure lineup at all types of semiconductor interfaces. These intrinsic IFIGS are the wave-function tails of electron states, which overlap a semiconductor band-gap exactly at the interface, so they originate from the quantum-mechanical tunnel effect. He shows that a more chemical view relates the IFIGS to the partial ionic character of the covalent interface-bonds and that the charge transfer across the interface may be modeled by generalizing Pauling's electronegativity concept. The IFIGS-and-electronegativity theory is used to quantitatively expl