Fully dense doped-ZnO varistors with sub-micrometer grain size (see Figure for a TEM image) can be fabricated by a strategic two-stage, one-cycle, thermal processing method at temperatures as low as 825 degreesC. The nonlinear coefficients alpha of such fully dense varistors are as high as 270, which is more than one order of magnitude higher than those currently given for commercial ZnO varistors.