Gd3Al2Ga3O12:Ce (GAGG:Ce) was studied by surface photovoltage spectroscopy using the ultraviolet photoelectron spectroscopy technique with synchrotron radiation and a laser source. The lowest Ce3+ 4f level is located below the conduction band minimum by 3.02 eV. This result is supported by the excitation spectrum for photo-stimulated luminescence and is compatible with the value predicted by the vacuum-referred binding energy scheme for GAGG:Ce. It is also found that GAGG:Ce is of the p-type. The information on the energy location of the Ce3+ 4f level and majority carrier type provides us with hints on how to improve the optical properties of GAGG:Ce for photonic device applications.