Experimental evidence for a charge-transfer excitation of Yb in InP on cubic lattice site YbIn is obtained from time-resolved photoluminescence spectra. The results strongly indicate that the Yb related electronic level EC−30 meV, up to now only considered to be an electron trap, is indeed the Yb3+/Yb2+ acceptor level. We conclude that this level plays the crucial role for effective excitation of the 4f emission of the Yb3+ ion in InP. The thermal quenching in photoluminescence and for the decay time is ascribed to hole emission from the excited Yb3+ ion into the valence band.