Using reflectance-difference spectroscopy, we determine surface-induced optical anisotropy (SIOA) spectra of clean, hydrogenated, and oxidized (113) and vicinal (001) Si surfaces to obtain a better understanding of the origin of the optical response of surfaces and interfaces. Hydrogenation was performed either by etching in dilute HF or by exposing clean surfaces to atomic hydrogen. Hydrogenated and oxidized vicinal surfaces show energy-derivativelike spectra that roughly scale with offcut angle, indicating step-induced behavior, and exhibiting features near 3.4 and 4.2 eV, the threshold energies of the (E(1), E(0)’) and E(2) interband critical points of bulk Si, respectively. The appearance of derivativelike line shapes indicates that bulk threshold energies become dichroic near the surface due to the surface-induced modification of the potential, as supported by model calculations. However, direct integration yields dielectric functions somewhat different from bulk values, indicating that the surface affects the near-surface dielectric function. SIOA spectra for clean surfaces are qualitatively different, exhibiting dielectric-functionlike line shapes that appear to originate primarily from terraces, although indications of smaller derivativelike contributions are also found.