The present disclosure provides a method of manufacturing a semiconductor device, including providing a semiconductor structure including a sequential stack of an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. A first metal layer and a second metal layer on the first metal layer are formed on the semiconductor structure. A heat treatment process is performed, such that the first metal layer is oxidized to form a first metal oxide layer and the second metal layer is reversed to form a second metallic compound layer between the first metal oxide layer and the p-type semiconductor layer. The first metal oxide layer and the second metallic compound layer are removed. A mesa etching process is performed after performing the heat treatment process, to form a mesa region exposing a part of the n-type semiconductor layer.