In this article, a detailed analysis of the wetetching technique for AlGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxidation plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation temperature and time. The correlation of etching roughness with oxidation time and temperature was investigated. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for AlGaN layer was given. In this article, a detailed analysis of the wetetching technique for AlGaN / GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxidation plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation temperature and time. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for AlGaN layer was given.