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To retain the advantageous properties of Al2O3 ceramics, their electrical conductivity must be controlled using a small amount of the conducting phase by pressure-less sintering in an air atmosphere. In this study, the electrical conductivity of Al2O3 ceramics was successfully increased from 10−16 to over 10° S/cm by precipitating a small amount of indium tin oxide (ITO) grain boundary phase. An ITO phase of only 3-mol% (4.45 vol. %) was propagated three-dimensionally in pressure-less sintered Al2O3. Electric discharge machining (EDM) showed the machinability of electrically conductive Al2O3/3-mole% ITO grain boundary composites. Furthermore, the temperature dependency of the electrical conductivity was identified as metallic, exhibiting an electrical conductivity that decreases slightly with increases in measurement temperature, as observed in metals and ITO. The temperature dependence of the electrical conductivity of ITO was maintained in the Al2O3/ITO grain boundary composites. [ABSTRACT FROM AUTHOR]