For the first time, a new phenomenon of transcon-ductance enhancement due to back bias found in submicron MOSFET's is reported. A two-dimensional numerical simulation has been performed to investigate the origin of this observation. The enhancement of the channel potential gradient is verified to be the main reason responsible for this anomalous transconductance enhancement effect. Moderate channel doping concentrations (5 × 1016 ~5 × 1017 cm-3) short channel lengths (submicron regime), and operation under small drain bias are three key conditions for the maximum transconductance enhancement due to the back bias to occur. A conventional linear I-V model, which employs an effective channel length defined by the source/drain metallurgical junctions and bias-independent source/drain extrinsic resistance is not able to predict such characteristics.