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» is given by the optical dielectric constant. Chemical trends are thus simply explained. © 1985 The American Physical Society.