Self-heating effect (SHE) is one of the key concerns for the reliability issues of SOI MOSFETs. The unavoidable SHE during HCI test may underestimate the devices performance and lead to the inaccurate lifetime prediction. In this paper, a new method is proposed to accurately predict the lifetime of 0.18 μm PD-SOI NMOS device based on DC HCI stress. The temperature increase (Tsh) caused by SHE is quantitatively extracted by gate resistance measurement. Then, the degradation part due to SHE is removed to accurately extrapolate lifetime of PD-SOI NMOSFET device using substrate/drain current ratio model. As a result, the extrapolated lifetime of 0.18 μm SOI NMOS illustrates a significant difference by 63.5% whether considering removal of SHE or not, indicating that the impact of SHE on the reliability issue of SOI device can not be ignored, otherwise leading to the inaccurate lifetime prediction.