Narrow band gap semiconductors of AIVBVI group are the most important materials for IR optoelectronics in the wavelength range of 0.74 ... 40 μm. The concentration of charge carriers in these compounds (PbTe, Pb1-xSnxTe) is determined by the degree of stoichiometry deviation; the vacant sites in the lead sub-lattice are acceptors, and in the tellurium sub-lattice are donors. According to the phase diagram, the PbTe stability region, depending on the compound stoichiometry of, is shifted to the tellurium side and at the crystallization the solid phase with a tellurium excess appears firstly. The holes concentration, which occur due to deviations from stoichiometry, reaches 1018-1019cm-3. This leads to the change of the electrical parameters of the given material along the single crystal ingots [1], therefore the problem of impurity states plays an important role in the problem in the fabrication of materials with the needed parameters [2]. The analysis of PbTe: Ga crystals galvanomagnetic phenomena shows that there are some instabilities of concentration and conductivity at the high voltages applied to the crystal. In the temperature range 54 - 100 K, the current-voltage characteristics were investigated in dependence on the rate of the voltage switching. The voltage variation rate has changed from 0.015 V / s to 2.5 V / s. It has been observed that the current-voltage characteristics have the N-type shape. So, there a sector with negative differential resistance exists. The emergence of this sector is due to the unipolar injection of the charge carriers from the ohmic contacts and their subsequent capture on the trap centers. The capture takes place by penetrating a columbian potential barrnone-linearier. At the electric field value increase, the charge carriers capture processes are more intensive. By coming from the theory of space charge limited currents, the energy position of the capture levels equal to 0.08 eV, related to the presence of the gallium impurity was determined.