We observe a light-induced on–off switching of the selective donor–acceptor pair excitation in bulk-grown semi-insulating GaAs. The spectral dependence of the switching process is related to the metastability of the EL2 defect. In the ground state, this As-antisite related midgap donor compensates the shallow acceptors and is responsible for the semi-insulating properties of the material. The loss of the shallow acceptor compensation, that accompanies the transfer of the EL2 to its metastable state leads to the observed absorption and luminescence quench of the shallow donor–acceptor pairs. We exploit these effects in demonstrating optical data storage in semi-insulating GaAs. ©1998 American Institute of Physics.