An MOS memory based on Si nano-crystals has been fabricated. We have developed a repeatable process of forming uniform, small-size and high-density Si nano crystals and spherical nano-crystals of about 4.5 nm in diameter with density of 5 x 10(11)/cm(2) were obtained. Threshold voltage shift of 0.48 V corresponding to single electron storage in individual nano-crystals is obtained. For the first time, room temperature single electron effects are observed. These prove the feasibility of practical Si nano-crystal memory.