A significant improvement (220%) is reported in the low voltage (2000 V) aging characteristics under cathodoluminescence (CL) excitation for ZnS phosphors coated with 1.0 wt % SiO2 by the sol-gel technique. The formation of nanoscale uniform coating was confirmed by structural analysis. An improvement in chemical and thermal stability was also confirmed by chemical etching and heat-treatment of the SiO2-coated phosphors. Also, the CL aging study showed a much improved CL efficiency curve for the SiO2-coated ZnS phosphors. The Auger electron spectroscopy study showed that the SiO2-coated phosphors were far more resistant to the loss of S species and to the formation of oxide dead layer. The structural, chemical, and CL characterizations demonstrated that the thin and uniform SiO2 lavers on ZnS phosphors served as protective layers retarding the surface-related degradation, which is critically important for the development of commercial field emission displays.