We have studied the electronic structure of potassium-covered Si(100)-(2 × 1) surfaces with angle-resolved direct (ultraviolet) and inverse photoemission at room temperature. Single-domain (2 × 1)-reconstructed surfaces were obtained by using vicinal samples. At a K coverage of less than 1 2 monolayer, an empty overlayer-derived state appears at 2.4 eV above the Fermi level. With increasing coverage it shifts downwards in energy and becomes dispersive. At saturation coverage, the surface is metallic owing to the filing of the minimum of this band, which has mainly K 4p2 character. Parabolic-like dispersion are observed for it in the ḡG-J̄′ and the ḡG-J̄ directions (i.e., both along and perpendicular to the dimer rows), showing the metallic bonding in the overlayer and a strong K-K interaction in both directions. Our results for saturation and near-saturation coverage at room temperature are consistent with atomic models having a full monolayer coverage of K atoms and a mainly covalent K-Si bonding. © 1992.