We have observed localized surface states (Tamm states) intentionally introduced in AlGaAs/GaAs superlattices by a terminating layer of AlAs. The formation of these states is manifested by excitonic interband transitions in photoluminescence excitation spectra. Critical confirmation is provided by photocurrent experiments under an electric field that show additional transitions as well as anticrossing interactions between the Tamm states and the Stark-ladder states associated with the superlattice.