Abstract: An optical memory comprising a doping modulated multilayer made of amorphous semiconductor, and at least two electrodes, one of the electrodes being transparent and the multilayer being sandwiched between two electrodes. Data is written by increasing the electrical conductance of the amorphous semiconductor by irradiating it is light. Data is erased by the application of a bias voltage to the electrodes and also by irradiating the amorphous semiconductor with light having photon energy of approximately half or less of the optical energy band gap of the amorphous semiconductor. The memory effect can be maintained for a week or longer, and the memory can be erased without heating the memory device, whereby the lifetime of the device is lengthened.