A method for direct silica-coating of fluorescent semiconductor nanoparticles is proposed. The fluorescent semiconductor nanoparticles used are quantum dots (Q-dots), which are CdSexTe1-x nanoparticles coated with ZnS and succeedingly surface-modified with amino groups. The silica-coating was performed in the presence of the Q-dots in 1-15M H2O, 0.4 x 10(-4)-40 x 10(-4) M NaOH and 0.5 x 10(-4)-50 x 10(-4) M tetraethyl orthosilicate (TEOS). Silica shells were formed at 5M H2O and 4 x 10(-4) M NaOH. Under these concentrations of H2O and NaOH, the particle size of silica-coated Q-dots could be varied from 15.8 to 31.7 nm as the TEOS concentration was increased from 2.5 x 10(-4) to 50 x 10(-4) M. The silica-coated Q-dots showed fluorescence as well as the uncoated Q-dots.