The tunnel cathode consists of a metal‐insulator‐metal sandwich in which the electrons tunnel through the insulator material. This paper presents an analysis of the noise associated with the space‐charge waves of a beam emitted from such a cathode. The beam noise temperature for a refrigerated tunnel cathode is shown to be 2730 &dgr;, where &dgr; is the value in volts of a built‐in energy window for the emitted electrons. The value of &dgr; is adjustable by means of a dc potential. Assuming a beam noise temperature of 30°K, the current density is calculated for a variety of cathode parameters. A discussion is presented of the significance of the parameters and of the difficulties which would be encountered in constructing such cathodes for low noise.