CdS quantum dots (QDs) were formed on ZnSe and ZnSxSe1-x. The nucleation process was monitored by reflection high energy electron diffraction, and it was suggested that QDs were formed without the wetting layer, The low temperature (13 K) photoluminescence (PL) measurement showed that the peak energy could be controlled by the amount of the CdS deposit. The PL peak energy covered most: of visible range, indicating that the band lineup between CdS QD and ZnSe (or ZnSxSe1-x) host would be type II. Bright green and blue light emitting diode (LED) structures were fabricated in which CdS QDs were embedded in pn junctions of ZnSe and ZnSxSe1-x. The control of QD size as well as the band gap of the host material enabled the luminescence peak wavelength of the LED to be varied.