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We present an experimental thermal memory with direct optical control and readout. Information is stored in the internal temperature of the device, while laser illumination is used to read, write, and erase stored bits. Our design is based on an absorptive optical resonance in a silicon photonic crystal slab. When the slab is illuminated by a laser with a wavelength close to the resonance, the optical absorption is nonlinear with power, resulting in thermo-optic bistability. We experimentally demonstrate bistability in a fabricated device and show the reading, writing, and erasing of a single memory bit. A hybrid optothermal model shows good agreement with the experiment. Time dependent measurements show that the experimental write/erase times are less than 500 µs. We demonstrate that memory reliability is maintained over 106 cycles, with less than 3% change in the transmission values for the memory ON and OFF states. Our approach allows operation in high temperature and/or highly fluctuating temperature environment up to 100 °C or greater.