In this paper we present a detailed investigation on the influence of carbon co-implantation in the source/drain extension on leakage current and defect density in PFET transistors. Carbon is used to reduce the transient enhanced boron diffusion, to decrease short channel effects and to control the overlap length of the transistor. Leakage currents are measured and separated in order to analyze the influence of the carbon on the different MOSFET regions. An increase in carbon dose by a factor of 1.15 leads to an enhanced source/drain extension leakage which is caused by carbon induced defects. No effect of the carbon implantation on source/drain junction leakage was found as the co-implant is located above the source/drain depletion region. In addition an increase of gate induced drain leakage with carbon dose was observed. This increase is further analyzed by charge pumping technique.