The steady‐state Nyquist theorem (or the steady‐state fluctuation‐dissipation theorem), which reduces to the Nyquist theorem in thermal equilibrium, is obtained for nondegenerate semiconductors by solving the Langevin‐type Boltzmann transport equations with the relaxation‐time approximation. This theorem is an extension of the Nyquist theorem to nonequilibrium systems for nondegenerate semiconductors. The derived theorem holds for any nondegenerate semiconductor device with one‐dimensional geometry when the quasi‐Fermi levels of electrons and holes can be defined for the steady‐state electron and hole distributions at any position inside the device, i.e., when at any position inside the device the steady‐state electron and hole distributions are not driven far away from the Maxwellian distributions. The derived theorem resembles almost exactly the functional form of the Nyquist theorem. As an application of this theorem the thermal noise in double‐injection space‐charge‐limited solid‐state diodes is calculated using this theorem.