We report on the reliability of the gate oxide on C-face of 4H-SiC. Constant current stress TDDB measurement shows that QBD of the gate oxide of f200 [μm] on C-face is as much as 18 [C/ cm2], which is much larger than the typical value (0.1[C/ cm2]) of that on Si-face of 4H-SiC. The lifetimes of the gate oxide under the electric field of 3[MV/cm] are roughly evaluated from the leakage characteristics and obtained QBD. The estimated lifetimes of the gate oxide of f600 [μm] are about 900 years. TDDB measurements of MOSs on two wafers, which have different dislocation densities, show that reliability of gate oxide on C-face is insensitive to the dislocation density. Meanwhile, reliability of the gate oxide is sensitive to the surface defect density: it is significantly degraded on the wafer, which has 2000 surface defects in a whole 2-inch wafer.