Abstract: In this work, we have investigated the deep trench etching and isolation technology applied to the monolithic integration of the silicon-based GaN. The etching parameters of the inductively coupled plasma（ICP） and the composition ratio of the etching gas（Cl₂ and BCl₃） have been optimized. The insulating dielectrics have been deposited in the deep trench by plasma enhanced chemical vapor deposition（PECVD） and plasma enhanced atomic layer deposition（PEALD）. The leakage current of the deep trench with SiO₂ deposition（～1 μA/mm） is one order of magnitude lower than the leakage current with ion implantation isolation（～10 μA/mm） at the limit voltage（200 V） of the GaN epitaxial layer（～1.8 μm）. Due to the uniform coverage and effective passivation of PEALD-Al₂O₃, the leakage current can be further decreased by one order of magnitude（～0.1 μA/mm）, which indicates the advantages of deep trench isolation. Therefore, this technology can promote the development and application of the monolithic integration of silicon-based GaN.