We explored the effect of K and K-Na substitution for Pb atoms in the lattice of PbTe, in an effort to test a hypothesis for the development of a resonant state that may enhance the thermoelectric power. At 300K the data can adequately be explained by a combination of a single and two-band model for the valence band of PbTe depending on hole density that varies in the range 1-15 x 10(19) cm(-3). A change in scattering mechanism was observed in the temperature dependence of the electrical conductivity, s, for samples concurrently doped with K and Na which results in significantly enhanced s at elevated temperatures and hence power factors. Thermal conductivity data provide evidence of a strong interaction between the light-and the heavy-hole valence bands at least up to 500K. Figure of merits as high as 1.3 at 700K were measured as a result of the enhanced power factors.