SiO₂ glass thin films doped with semiconductor microcrystals such as CdSe, CdTe and GaAs were prepared by the rf-sputtering technique. The concentration and mean diameter of the microcrystals were dependent on the relative surface area of the semiconductor chips on SiO₂ glass target plate, and the size distribution was strongly influenced by the sputtering condition. The suitable condition for each semiconductor has to be individually determined. The quantum size effect was found from the blue shift of the optical absorption edge. The shift for CdSe-doped SiO₂ glass thin films clearly deviated from the simple theoretical predictions based on the confined effects. Thus, introduction of Coulomb interaction and the influence of the dielectric constant of matrix were found to be necessary to interpret the experimental data.