We report a large piezoresistive effect of the plasma assisted chemical vapor deposited hydrogenated amorphous carbon (a-C:H) films deposited at bias voltages of - 350 and - 800 V. The gauge factors were measured in transversal, longitudinal strain configurations and lateral, vertical current flow directions with respect to the layer surface. The gauge factor measurements were performed in the temperature range of 23-60 degrees C. A model is proposed to explain the origin of piezoresistive effect in the a-C:H films. From the experimental results we suggest the parameters which can further enhance the gauge factor values in the films. (C) 2007 Elsevier B.V. All rights reserved.