Diamond has many properties which make it ideal for a high power solid-state switch. The crystal structure of diamond is relatively well characterized. It is a semiconductor with a band-gap of 5.5 eV at 3000 K. The high band-gap of diamond results in a small dark current compared to Si or GaAs. As a result the breakdown field or holding voltage is very high, 1-1 0 MV/cm. The electron and hole mobility are approximately 2000 cm2/V-sec. At room temperature, diamond has the highest thermal conductivity of any solid, 20 W/OK -cm, about five times that of copper. This is ideal for switching because heat dissipation and thermal runaway problems are greatly mitigated. Our switch concept uses a low current (<1A/cm2), 100- 150 keV electron beam to control the diamond switch. Electron beam control offers much higher efficiency and flexibility than laser control. We obtained experimental results1 with electron beam activated diamond films which were CVD grown on an n-type silicon substrate. With the substrate biased positive, the switch current was found to follow the electron beam pulse up to fields of about 0.9 MV/cm where "lock-on"occurred, i.e., the switch current continued to flow even after the electron beam was turned off. This effect, most likely due to double charge injection, was suppressed by biasing the n-silicon substrate negatively. The switch current then followed the electron beam pulse up to electric fields of 1.8 MV/cm, limited by our electrical circuit, with no evidence of "lock-on." The predictable response of the switch current to the electron beam pulse at extreme applied fields make electron beam controlled diamond switch a promising candidate for a high power on-off switch. Steady advancements in CVD polycrystalline and single crystal diamond2 help make this possible.