We present a study on the modification of the electronic structure and hole-doping effect for the layered dichalcogenide WSe2 with a multi-valley band structure, where Ta is doped on the W site along with a partial substitution of Te for its lighter counterpart Se. By means of bandstructure calculations and specific-heat measurements, the introduction of Te is theoretically and experimentally found to change the electronic states in WSe2. While in WSe2 the valence-band maximum is located at the Γ point, the introduction of Te raises the bands at the K point with respect to the Γ point. In addition, thermal-transport measurements reveal a smaller thermal conductivity at room temperature of W1−xTaxSe1.6Te0.4 than reported for W1−xTaxSe2. However, when approaching 900 K, the thermal conductivities of both systems converge while the resistivity in W1−xTaxSe1.6Te0.4 is larger than in W1−xTaxSe2, leading to comparable but slightly smaller values of the figure of merit in W1−xTaxSe1.6Te0.4.