We have investigated the formation of self-organized CdSe quantum dots (QDs) on ZnSe(100) surfaces with the use of photoluminesence (PL) and transmission electron microscopy (TEM). TEM measurement reveals that CdSe grows two-dimensionally on ZnSe(100) surfaces in the initial stages, and then at around 1.8 monolayer (ML), CdSe grows three-dimensionally and begins to nucleate QDs. Coherent CdSe QDs are naturally formed on ZnSe surfaces, when the thickness of CdSe layers is about 2 ML. The plan-view TEM images reveal that CdSe QDs have a relatively narrow distribution of QD size, and that the density and diameter of CdSe QDs are about 10(10) cm(-2) and 30 nm, respectively. Moreover, CdSe QDs exhibit a strong green emission even at room temperature.