Tantalum substitutions up to 5 atomic per cent (a/o) of the cations have been made in the three Group VIB dichalcogenides, , , and . Tantalum‐substituted p‐type had the best thermoelectric properties with a figure of merit about . Substitution of a number of other elements was attempted in the compounds and , but only the Group VB metals were sufficiently soluble to give p‐type materials with electrical conductivities at useful levels. Hall coefficient measurements were made on all three of the above‐mentioned compounds, and was shown to have the highest carrier mobility (100 cm2/v‐sec); this explains its superior thermoelectric properties. An excellent correlation is shown between Seebeck coefficient measurements and Hall coefficient measurements for the family of compositions for an effective mass ratio of 1.0 with the assumption of an ionic lattice scattering mechanism.