A theoretical analysis for the noise temperature of a low‐temperature hot‐electron superconducting mixer has been presented. The contribution of both Johnson noise and electron temperature fluctuations has been evaluated. The theoretical limit of the single‐side band noise temperature of the device due to the intrinsic noise mechanisms has been estimated to be as low as 20–40 K, depending on the film material. The corresponding noise bandwidth can be as large as 2–3 GHz, for a device with the electron‐phonon cooling mechanism. An improvement of the sensitivity is not necessarily followed by a decrease of the mixer conversion gain bandwidth.