The photocapacitance (PC) technique allows the determination of deep‐level as well as surface states at semiconductor/electrolyte (SC/EL) contacts. Expressions of the PC signal, given in several peculiar cases, help in the understanding of the results obtained with GaAs in contact with an aqueous electrolyte. It is found that relevant experimental conditions of band bending and/or incident photon flux are required to detect transitions which have a small magnitude compared to the large response due to EL2 in GaAs. A quantitative interpretation of the spectrum is also given.