Angle-resolved photoemission techniques were used to study GaAs(100) surfaces grown by molecular-beam epitaxy. Three well-ordered surfaces with the c (4×4), c (2×8), and c (6×4) reconstructed surface structures and a disordered As-covered (1×1) surface were investigated in the photon-energy range of 12-70 eV. All major sharp peaks in the normal-emission spectra were found to be transitions from bulk valence bands; therefore, transitions due to surface states were either weak or broad. The variations in bulk-peak intensities for different surface structures were related to surface diffraction effects. For photon energies greater than about 20 eV, primary-cone peaks for transitions from the upper bulk valence bands to a broadened and shifted free-electron-like final band were identified, and energy dispersion relations for the upper valence bands were determined along the  direction. Surface umklapp transitions were quite strong due to the presence of many short surface reciprocal-lattice vectors. To characterize these surfaces, angle-integrated photo-emission measurements of valence bands and core levels were made, and the positions of the Fermi level for these surfaces were determined. © 1983 The American Physical Society.