It has been proven that in two-valley semiconductors, in the presence of a temperature gradient, a thermomagnetic wave is excited, which propagates perpendicularly to the temperature gradient. Such an unstable wave is excited at an electric field value in which ionization, recombination and generation do not occur. Then the total concentration of charge carriers is constant. The Gunn effect in GaAs was discovered when there are ohmic contacts in the sample. It is difficult to obtain ohmic contacts in the experiment and therefore it is necessary to consider the injection of charge carriers on the contacts. It is necessary to calculate the impedance of the crystal in the presence of injection and determine the capacitive and inductive nature of the impedance. The excited wave in GaAs in the case under consideration depends on the frequency of hydrodynamic wave. The electric field carries out between valleys The Gunn effect was discovered in GaAs at values of crystals of the [100] axes. At other values of the crystalline axes, the frequency and growth increment will have other values. In our theoretical study, an isotropic sam-ple was used, following Gunn's experiments. Of course, theoretical studies in anisotropic samples are of scientific interest.