An analysis of the parameters governing the performance of a sputter‐ion pump leak detector using oxygen or helium as the probe gas is presented. It is shown that the smallest detectable leak is proportional to the stability of the pump current and to the pressure. For optimum performance the pump control unit has to be voltage‐stabilized. Expressions for the leak rate and minimum detectable leak in terms of the change of pump current are derived which predict an ultimate capability at least equal to that of conventional mass spectrometer leak detectors. This was confirmed experimentally.