In this work, we successfully achieve a hysteresis-free negative capacitance field effect transistors (NCFETs) by exploiting a defect passivation scheme. This research work simultaneously provides a new insight into the gate-oxide stress reliability of NCFET. The fluorine-passivated HfAlOx NCFET shows the excellent transistor characteristics including a steep subthreshold swing of sub-30-mV/dec, a negligible hysteresis-free switch of ∼10mV and a large on/off current reatio (Ion/Ioff) of >107. Most importantly, fluorine passivation for NC HfAlOx effectively suppress the generation of shallow traps during electrical stress test. Besides, it is favorable to maintain NC operation and SILC immunity by in-situ fluorine passivation, which has been verified by transient pulse I-V measurement.