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Time-dependent dielectric breakdown (TDDB) is one of the major issues concerning long-range reliability of dielectric layers in SiC-based high-power devices. Despite the extensive research on TDDB of SiO2 layers on Si, there is a lack of high-quality statistical TDDB data of SiO2 layers on SiC. This paper presents comprehensive TDDB data of 4H-SiC capacitors with a SiO2 gate insulator collected over a wide range of electric fields and temperatures. The results show that at low fields, the electric field acceleration parameter is between 2.07 and 3.22 cm/MV. At fields higher than 8.5 MV/cm, the electric field acceleration parameter is about 4.6 cm/MV, indicating a different failure mechanism under high electric field stress. Thus, lifetime extrapolation must be based on failure data collected below 8.5 MV/cm. Temperature acceleration follows the Arrhenius model with activation energy of about 1 eV, similar to thick SiO2 layers on Si. Based on these experimental data, we propose an accurate model for lifetime assessment of 4H-SiC MOS devices considering electric field and temperature acceleration, area, and failure rate percentile scaling. It is also demonstrated that temperatures as high as 365degC can be used to accelerate TDDB of SiC devices at the wafer level.