A model is presented for the mechanism which establishes the dynamic equilibrium cesium coverage on a W(110) converter surface in the discharge chamber of a negative hydrogen ion source. The charge state of cesium particles arriving at the converter surface is found to be a crucial parameter. A coverage greater than 0.26 monolayers cannot be maintained if the cesium component is highly ionized. The corresponding negative hydrogen ion formation probability is far from optimum. This situation is probably present in all high‐density surface conversion negative ion sources employed nowadays.