This study on utilizing HV-CV analysis to investigate the correlation between defect generation regions and field plates in pGaN HEMT. The FPs can reduce surface field and improve VBD, but it may introduce complexities trapping behavior in HTRB. However, we used HV-CV to demonstrate that the presence of C impurities in the buffer layer results in positive and negative charge redistribution. Furthermore, optimizing process enhances performance and reliability, particularly below the FPs near the gate.