In the present study, we comparatively investigate the distribution of electronic interface states of three different perovskite oxide interfaces, formed by epitaxial thin films of La_0.7Sr_0.3MnO ₃ (LSMO), La_0.7Ca_0.3MnO₃ (LCMO), and La_0.7Ce_0.3MnO₃ (LCeMO) on SrTiO ₃(100) substrates, in the as-prepared state as well as after an annealing procedure. We find that annealing significantly reduces the number and density of interface trap states. Two different experimental realizations of the surface photovoltage spectroscopy (SPS) technique were employed: an approach based on X-ray photoelectron spectroscopy (XPS), as well as a capacitive method. The advantages and limitations of both methods are critically discussed.