Thermal post deposition treatments are applied to DC-sputtered aluminum-doped zinc oxide (ZnO:Al) films and lead to a significant improvement of the electrical properties. Protective layers of amorphous silicon are used to protect the films from degradation during the high temperature treatment. Annealing for 6 hours at 500 degrees C leads to a carrier mobility of 48 cm(2)/Vs at a carrier concentration of 5.5 . 10(20) cm(-3). Furthermore, improvements in the optical as well as in the electrical properties are possible at the same time compared to the as-deposited film. This is achieved by carrying out two thermal treatments to the ZnO:Al film, one prior to the capping with the protective layer and one afterwards. A series of samples with different carrier concentrations allows us to draw conclusions on the specific electrical transport properties. (C) 2011 Elsevier B.V. All rights reserved.