Charge stored in an insulating layer on a semiconductor can influence the field at the surface of the semiconductor and consequently control the surface recombination velocity. This paper describes the use of this effect to control the current in a reverse‐biasedp‐njunction in the semiconductor. When an electron beam is used to write and read the stored charge, the effect can be used to produce high‐resolution high‐gain devices that have a variety of potential uses in information‐storage applications. Experiments demonstrating this effect are described.