The conditions necessary to establish a stable hollow‐cathode or cavity mode in a high‐pressure mercury vapor discharge have been studied by analysis of the physical processes at the electrodes. The electron emission is primarily Schottky‐enhanced thermionic, so the cavity mode is favored by a thermally shielded cavity design, at low currents. Techniques have been developed for measurement of the temperature of the arc terminus of the probe contact potential relative to the electrode, of the cathode fall of potential, and of the power input to the electrode. Positive ion current densities, work functions of the dispenser‐type electrode at the arc terminus and other interesting quantities have been obtained by computation. The analysis giving these results has been partially verified by experiment.