Noise quantities at the potential minimum in the high‐frequency diode are analyzed by means of a relatively simple model which assumes that the transit angle from the cathode to the potential minimum is small and that the transit angle from the potential minimum to the anode is large. The mean‐square convection current is found to be about half full shot noise for a typical case and the mean‐square velocity is found to be the same as in the temperature‐limited case. Application of this result to an analysis of the minimum obtainable noise figure of klystrons and traveling‐wave tubes using velocity‐jump noise reduction shows that their noise figure can be reduced without theoretical limit by increasing the current density at the cathode.