A semiconductor element having a high breakdown voltage includes a substrate, a buffer layer, a semiconductor composite layer and a bias electrode. The buffer layer disposed on the substrate includes a high edge dislocation defect density area. The semiconductor composite layer disposed on the buffer layer includes a second high edge dislocation defect density area formed due to the first high edge dislocation defect density area. The bias electrode is disposed on the semiconductor composite layer. A virtual gate effect of defect energy level capturing electrons is generated due to the first and second high edge dislocation defect density areas, such that an extended depletion region expanded from the bias electrode is formed at the semiconductor composite layer. When the bias electrode receives a reverse bias, the extended depletion region reduces a leakage current and increases the breakdown voltage of the semiconductor element.