Zn-Sb systems are interesting as thermoelectric materials because the elements are relatively cheap and show low toxicity. In this work, a high thermoelectric figure of merit of 1.15 at 670 K is obtained in a p-type Ag-doped ZnSb nanostructured with in situ formed Ag3Sb because of its optimized carrier concentration and a significant reduction in lattice thermal conductivity. The samples also exhibit good thermal stability. The results here suggest that ZnSb is an efficient, stable and low-cost thermoelectric material and deserves more attention. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.