Various models of Schottky-barrier formation suggest Fermi-level pinning in midgap. Elemen- tary band-structure considerations indicate that, for diamond-structure semiconductors, the physically relevant gap is the indirect gap, corrected for spin-orbit splitting. Schottky-barrier heights for elemental and III-V compound semiconductors can be predicted to 0.1 eV from measured indirect gaps and splittings. The dimensionless pinning strength S\ifmmode\bar\else\textasciimacron\fi{} is given by the optical dielectric constant. Chemical trends are thus simply explained.