The phenomenon of avalanche breakdown in silicon devices is often accompanied by a current into insulating layers leading to serious degradation, on the one hand, or to practical use in nonvolatile memories on the other hand. By injection of hot electrons towards the gate of a metal‐oxide semiconductor (MOS) device, the oxide and/or floating gate is charged. The large initial current is rapidly reduced by this space charge. By removing the oxide at the site of injection, in a structure optimized for its purpose, the electron current can be injected into vacuum. Lowering the work function with, e.g., cesium enhances the vacuum current several orders of magnitude to levels where it can be of practical use. This use is demonstrated in a simple (small) TV tube which already operates hundreds of hours without appreciable degradation. Basic principles and design aspects as well as technological aspects are discussed.