CdS quantum dot (QD) structures were grown by molecular beam epitaxy on (001) ZnSe. Circular QDs were observed from the sample, grown at 220 degrees C, whereas rectangular QDs were observed from the sample grown at 280 degrees C. The difference of the dot shape may be related to the metastable nature of CdS since CdS thin films grown at 220 degrees C show zincblende structures and thin films grown at 280 degrees C show wurtzite structures. The PL peak position and linewidth were strongly affected by the growth condition of QDs; QD samples with a thicker CdS deposition showed redshifts of the peak position along with the narrowing of the linewidth.