We have investigated formation and optical properties of single-layer and stacked self-assembled CdSe quantum dots (QDs) by reflection high-energy electron diffraction (RHEED), plan-view transmission electron microscope (TEM) image, and photoluminescence (PQ spectra. We have demonstrated a useful technique to control the dot size using the RHEED intensity observation during CdSe growth. The RHEED intensity significantly changes with the increase of CdSe coverage. The TEM observation reveals that the dot structures are formed at the minimum of the RHEED intensity variation. Using this technique, we have fabricated stacked QDs. The excitation power dependence of the PL spectra indicates the vertically coupling effect on thin ZnSe spacer samples.