Interest in semiconductor compounds of type А4В6.has quickened in the past few years. This is explained by the fact that these materials are basic materials for infrared devices and high-temperature thermoelectric applications and that given materials doped with elements of group III exhibit a number of features in their electrophysical, thermoelectrical and optical properties [1,2]. This explains the interest in these materials and, in particular, in semiconductor compound Pb1-хTlхTe as the most striking example in which a lot of unique properties have been observed [1,2]. Thin singlecrystal wires of Pb1-x-yTlxNayTe (x=0.001 ÷ 0.02, y=0÷0.02, d = 5 ÷ 100 μm) were grown by the microcapilary high pressure injection and directional crystallization methods. The structural quality was tested by X-ray diffraction and Laser Microprobe Mass Analyzer (LAMMA). The thermoelectric properties of thin singlecrystal wires of Pb1-x-yTlxNayTe were studied in the temperature range 4.2 ÷ 300 K. Previously, it was demonstrated that for the samples corresponding to the chemical composition with the concentration of thallium 0.0025 < x <0.005 double sign reversal of thermoelectric power is observed [3]. In pure samples and samples with thallium concentration more than 1 at.%, thermoelectric power is positive in the whole temperature range. It is known that, in strongly degenerate samples in the conditions of resonant scattering, the value of the coefficient of thermoelectric power is determined by dispersion parameter, and for thermoelectric power determined by resonant scattering:formulawhere m is the chemical potential,e i is the mid position of the impurity band, G its width, Δ=εi-μ. The analysis of this formula allows describing features observed on the dependence of thermoelectric power on the concentration of an impurity in system Pb1-хTlхTe [3]. The formula is valid for sufficiently low temperatures (κT<<Γ). The second term in this formula is signvariable depending on relative position of the Fermi level and the middle of the impurity band. At Δ<0 the sign of the thermoelectric power can become abnormal. With a rise in temperature (κT ≥Γ) the selectivity of dispersion of carriers decreases that leads to the restoration of a normal sign of the thermoelectric power (for a high concentration of thallium impurity). The analysis of the formula allows drawing one more interesting conclusion: at middle transition of the impurity band by the Fermi level Δ> 0. This means that the sign of the diffusion thermoelectric power and the thermoelectric power caused by resonant dispersion coincide, which, in turn, should lead to significant increase in the total thermoelectric power. However, it is impossible to obtain a level occupation of the impurity band by more than one-half via doping only with thallium, [1,2]. For middle transition of the impurity band, additional doping with an acceptor impurity, for example sodium, is usually used [1,2]. The analysis of temperature dependences of thermoelectric power shows that simultaneous doping of the lead telluride with thallium and sodium leads to an increase in the thermoelectric power, and at a high concentration of the additional acceptor impurity (upon withdrawal of the Fermi level from the limits of impurity band of thallium) a restoration of the normal sign of thermoelectric power is observed, which is in agreement with the formula (1).