The hot-carrier effects of non-planar tri-gate SOI FET (TGFET) with back-gate bias were investigated. Negative back gate bias could raise the influence of buried oxide defects and then degrade the device quickly. For TGFETs with ultra-narrow fin width and side gate extension, the smaller buried oxide interface area and more obvious screening effect terminate the field lines to obviate the back gate bias efficiently. The extrapolated hot-carrier lifetime encourages the TGFETs as promising sub-10nm devices