An igniter plug is disclosed for use in jet and other internal combustion engines. The igniter plug has a center electrode having a firing tip, which is mounted within an insulator which in turn is mounted within an exterior metal shell. A ground electrode is integral with or in electrical contact relationship with the metal shell and is disposed in a spaced, spark gap relation with the firing tip of the center electrode. An electrically semiconducting surface is disposed adjacent the spark gap and in electrical contact with the center electrode and with the ground electrode. The electrically semiconducting surface is formed by a sintered ceramic body having an actual density of more than 95 percent of its theoretical maximum density, and consists essentially of 67-80 wt % of silicon carbide particles and 20-33 percent by weight of grain boundary phase of alumina particles, as well as one or more sintering aids selected from magnesia, silica or calcia. Not only is the density of the sintered ceramic body high, it is uniform. This uniform density provides for uniform electrical characteristics and increased resistance to erosion due to electrical discharges between the electrodes. The high and uniform density of the sintered ceramic body is obtained by applying pressure to the ceramic body only after reaching the sintering temperature.