One embodiment relates to a high-voltage electron gun including an insulator stand-off having a resistive layer. The resistive layer is at least on an interior surface of the insulator stand-off. A cathode holder is coupled to one end of the insulator 115 stand-off, and an anode is coupled to the other end. The resistive layer advantageously increases the surface breakdown field strength for the insulator stand-off and so enables a compact design for the high-voltage electron gun. Other embodiments, aspects and feature are also disclosed.