In this work, for the first time, an abnormal leakage current has been observed in MOSFET with 50nm channel length and beyond. This effect shows that, in an ultra-short channel MOSFET, sub-threshold swing (SS) and Ioff are decreased for back-biased nMOSFET and pMOSFET. This effect is attributed to the BJT-induced current from the source to the drain. An experimental approach has been used to verify the existence of this BJT current component. As a consequence, this BJT current can be reduced with appropriate control of the SID-to-substrate junction. As an application of the approach to advanced embedded-SiC MOSFET with various splits, it was found that a higher band-offset of SID-to-substrate junction will give rise to a larger the BJT ballistic transport current. This provides us important information on reducing the leakage current for advanced CMOS with 50nm and beyond.