Selectively grown ZnSe/ZnS photonic dot structures on (001)GaAs were studied with metalorganic molecular-beam epitaxy (MOMBE). ZnSe/ZnS photonic dots have four smooth {034} facets. These photonic dot structures show the optical resonances by microreflection measurements and act as three-dimensionally confined optical cavities. For controlling the position of the ZnSe active layer, the initial growth process of the ZnS dot structure was studied. It was found that the delay of the growth initiation exists in the small-area selective growth. Optical properties of the ZnSe/ZnS photonic dots were also discussed and weak modulation of the spontaneous emission by optical resonance was observed by the microphotoluminescence measurements. The luminescence was superimposed with the one from the ZnSe layers grown on the {034} ZnS side facets which were not coupled with the cavity modes. The modulation effects were much improved by etching the external ZnSe layers on the {034} ZnS facets.