Electronic and band properties of PbTe and Pb1-xSnxTe with x = 0.20, 0
.25, and 0.30 have been studied experimentally by a method involving a
field effect in electrolytes. The band gaps have been determined. The
effective masses of the densities of electron and hole states at the
surface in the space-charge region of these materials have also been d
etermined. The dispersion relation of the allowed bands near the surfa
ce in the PbTe and Pb1-xSnxTe can be described satisfactorily by a par
abolic model.