In-house developed (1-100) and (11-20) oriented 4H-SiC wafers, and a reference wafer were used to evaluate the impact of the SiC structural defects on the degradation phenomenon of bipolar pn diodes. Evaluation of the crystal quality and the degraded devices were performed by comparing the results of etch pit densities, electroluminescence, Berg-Baffett topography, HRXRD and HRTEM analysis. Our data demonstrate that the degradation phenomenon is strongly related to the SiC structural crystal defects of the starting material. DENSO (HQ) wafers are less susceptible to the forward current degradation, which we attributed to comparatively much lower etch pit densities, specially the slip/stacking fault defects.