Photonic signals were efficiently stored in a semiconductor-based memory cell. The incident photons were converted to electron-hole pairs that were locally stored in a quantum well that was Laterally modulated by a field-effect tunable electrostatic superlattice. At Large superlattice potential amplitudes, these pairs were stored for a time that was at least five orders of magnitude Longer than their natural Lifetime. At an arbitrarily chosen time, they were released in a short and intense flash of incoherent light, which was triggered by flattening the superlattice amplitude.