A high current surface discharge across the surface of an insulator in high vacuum is investigated. The mass erosion of the insulator and its surface voltage holdoff recovery are the two most important parameters of this investigation. Typically, the discharge current reaches approximately 350 kA peak with a pulse length of approximately 60 microsecond(s) (approximately 5 periods of a damped sinusoidal pulse). The vacuum level is maintained at approximately 10-6 Torr. The insulator materials tested include a variety of polymeric (i.e., polyethylene, nylon, epoxy-fiberglass composites, and polyurethane) and ceramic (alumina, silicon nitride, and zirconia) insulators. Insulator mass erosion and surface voltage holdoff recovery versus electrode material has also been investigated. The electrode materials used include stainless steel, molybdenum, copper, copper-tungsten, brass, aluminum, and lead. Insulator materials that have low mass erosion and good surface voltage holdoff recovery have potential applications in high power vacuum switches. Breakdown voltage histories and mass erosion data were obtained for the plastics, but only breakdown voltages were obtained for the ceramics.