In this article, a semi-insulating polycrystalline silicon (SIPOS)-SiO2 compound sheet is used for the first time as a passivating layer of a 4H-SiC n+pp+ structure. After the deposition of SIPOS by LPCVD, a unique thermal oxidation step, annealing in oxygen atmosphere at 900 °C instead of the normal method of oxide layer deposition, is adopted to grow an SiO2 layer over it. The passivation result demonstrates the reasonableness of the alternation. Moreover, chief technological parameters that influence the passivating effect are adjusted and conclusions are drawn that there should be excess oxygen in the SIPOS layer and its deposition temperature should be lower than 1000 °C. The annealing temperature should be high, up to 900 °C. Experimental data show that a SIPOS-SiO2 compound layer can act as an effective passivation sheet of the 4H-SiC n+pp+ structure to obtain an ideal breakdown voltage and leakage current.