Te-impurity-incorporated Sb 2 Te 3 , i.e., Sb 2 Te 3 + x mol % Te (x = 0, 4, 6, and 9) composites were synthesized by solid-state reaction technique. Analysis of x-ray diffraction indicates not only Te impurity as a second phase but also doping of Te via suppression of inherent Te vacancies in the Sb 2 Te 3 matrix. As a result of this doping and of the change in formation energy of different types of native defects in Sb 2 Te 3 due to synthesis in a Te-rich condition, carrier concentration (n H) lower than the pristine sample was observed. Low n H along with gradual convergence of valence bands due to progressive suppression of Te vacancies increases the Seebeck coefficient (S) in Te-incorporated samples. Even though Te impurities increase electrical resistivity (ρ), enhanced texturing of lattice planes ensures that charge carrier mobility does not degrade due to Te addition. As a result, a maximum power factor = 17 μW cm −1 K −2 at T = 480 K for x = 6 has been achieved. In addition, Te addition strengthens phonon scattering via an increase of phonon-phonon Umklapp scattering and point-defect-induced scattering of phonons. Due to such a strong phonon scattering, thermal conductivity (κ) decreases, and a reduced lattice thermal conductivity (κ L), as low as 0.28 W m −1 K −1 at 500 K for x = 6, has been achieved. As a result of simultaneous increase of S and decrease of κ, a high ZT ∼0.87 at 480 K, almost 33% higher than that of the host material, has been achieved.