The evolution of the compressive stress in Mo/MoOx sputter-deposited thin films has been followed in situ during deposition as a function of two parameters: the oxygen flux and the negative voltage bias applied to the substrate. In addition the microstructure of the films has been characterized. Oxygen accumulation at the interface was observed. We describe the origins of the stress in terms of ion bombardment and oxygen incorporation. (C) 2012 Elsevier B. V. All rights reserved.