A varistor comprises a primary varistor metal oxide, aluminum in an amount of about 1 to about 30 parts per million (ppm), about 0.1 to about 0.5 mole % bismuth, about 0.1 to about 1.5 mole % antimony, about 0.1 to about 1 mole % chromium, about 0.1 to about 1.0 mole % manganese, about 0.1 to about 2.0 mole % cobalt, and about 0 to about 1.0 mole % boron. Each of these elements is present in the form of its oxide and the varistor has a DC leakage current at 80% of V.sub.1ma/cm.spsb.2 of less than 1.0.times.10.sup.-7 amp/cm.sup.2.