A procedure to analyze the effect of the MOSFET drain-bulk junction tunneling current at high frequencies is presented. This procedure allows identifying the presence of band-to-band tunneling in short channel-length MOSFETs at different drain-to-source voltages. Since this analysis is based on experimental S-parameters performed to a single MOSFET, the procedure is not affected by the variations occurring in devices with different geometries. Excellent correlation between simulated and experimental output impedance for a 0.1 lm channel-length bulk MOSFET up to 40 GHz demonstrates the validity of the proposed technique.