Experimental data are reported for the persistent photocapacitance quenching observed at 77 K in GaAs. This effect, which arises on the so‐called oxygen (or EL2) center in gallium arsenide, is explained by the existence of two states of this center. The physical parameters of these stable and metastable states are given: optical cross section, annealing, and electrical deexcitation. Assuming a large lattice relaxation for the metastable one, a physical model is given with a possible microscopic origin. Other striking memory effects, and especially photoconductivity, are shown to be simply explained by our model.