In this letter, an n-type short-channel negative capacitance FinFET (NC-FinFET) with a hysteresis window of 0.48 V, an on-/off-current ratio of 107, and a sub-20-mV/decade average subthreshold slope (SSavg) that is intended to overcome the Boltzmann limit (i.e., the physical limit in the SS, which is 60 mV/decade at 300 K), is experimentally demonstrated vs. a baseline FinFET with an SSavg of ~105 mV/decade. In our testing, we confirmed that the large hysteresis window in a short-channel NC-FinFET can be suppressed by using an appropriate source/drain extension length ( $\text {L}_{\text {ext}})$ . As $\text {L}_{\text {ext}}$ in the NC-FinFET is increased, the gate-to-source/drain capacitance ( $\text {C}_{\text {GS}}/\text {C}_{\text {GD}})$ decreased and the hysteresis window narrows.