Hydrogen is an indispensable ingredient in integrated-circuit fabrication, since it is used to passivate defects at the Si/SiO(2) interface present in every CMOS transistor. Hydrogen will likely play an equally important role for the novel channel materials and dielectrics that are currently being investigated. We show that first-principles calculations can produce fundamental information about the behavior of hydrogen in relevant semiconductors and oxides. We point out the link between the electronic structure of hydrogen and the band-alignment problem, and specifically highlight why hydrogen at interfaces with germanium will exhibit a very different behavior from what is known to happen in silicon. (C) 2008 Elsevier B.V. All rights reserved.