High quality c-axis-oriented Ca3Co4O9 thin films have been grown on Si substrates using pulsed laser deposition under different oxygen pressures. The morphology and interface structure of the films have been investigated. It is shown that the films grow in such a way that the c-axis lies parallel to the substrate surface so as to minimize interface stress. Compared with their polycrystalline bulk counterpart, the thin film samples have a larger Seebeck coefficient and a lower resistivity. As a result the power factor increases significantly and reaches 0.21 mW/m K-2 at room temperature. (C) 2013 Elsevier B. V. All rights reserved.