In this work, we experimentally investigate the impact of measurement speed (μs-800 ps) on the characterization of reliability behaviors, hot carrier injection (HCI) and positive bias temerature instability (PBTI), for FDSOI nMOSFETs. The results show that, due to the severe self-heating effect (SHE) in the FDSOI nMOSFETs, the I-V measurement speed could significantly affects the characterization of threshold voltage V_th shift and saturation drive current I_dsat degradation after HCI and PBTI stress. Due to the inevitable SHE in the transistor channel caused by the long measurement time, the V_th shift and I_dsat degradation would be underestimated, leading to an overestimation of the HCI and PBTI lifetime. To precisely characterize the SHE-free reliability behaviors in FDSOI or FinFETs, a nanosecond-level measurement speed would be necessary to eliminate the SHE.