Surface photovoltage (SPV) measurements are traditionally carried out under steady-state conditions to determine the minority carrier diffusion length. While this technique is very convenient for bulk wafer defect characterization, especially the detection of iron in boron-doped silicon wafers, it is poorly suited to characterize epitaxial layers that are typically much thinner than the minority carrier diffusion length. We have developed the theory for frequency-dependent SPV measurements and have verified this theory with experimental data. We consider the various recombination/generation components in the semiconductor and determine the dependence on photon flux density, optical absorption coefficient, doping density, recombination lifetime, and temperature. Epitaxial layers are usually measured with techniques that are sensitive to generation parameters confined to the reverse-biased space-charge region (scr). We show that optical excitation can be used for scr confined recombination measurements, but the resultant lifetime is an effective lifetime incorporating both scr and surface recombination, heavily influenced by surface recombination.