Hot-carrier effects (HCEs) in fully depleted body-tied FinFETs were investigated by measuring the impact-ionization current. To understand the hot-carrier degradation mechanism, stress damages were characterized, by dc hot-carrier stress measurement for various stress conditions and fin widths. The measurement results show that the generation of interface states is a more dominant degradation mechanism than oxide-trapped charges for FinFETs with a gate-oxide thickness of 1.7 nm. It was found that a parasitic voltage drop due to a significant source/drain extension resistance plays an important role in suppressing the HCEs at narrow fin widths. This letter can provide insight determining the worst stress condition for estimating the lifetime and optimizing between reliability and ON-state drain-currents.