Metal/semiconductor heterojunctions have attracted interest for many years due to their importance in electronic device applications. Usually, owing to a large lattice mismatch between semiconductors and most metals, it is difficult to obtain a high-quality epitaxial interface by direct deposition of metals on semiconductors. In this work, we address this problem by proposing a novel strategy to use metal oxides as templates. Due to the small lattice mismatch between CoO and GaN, it was found that epitaxial CoO films can be readily formed on GaN. Subsequent decomposition of CoO at high temperature and low oxygen pressure gives rise to an epitaxial metal Co film on GaN, forming a Co/GaN interface of good quality, and the inheritance of the orientation relationship between CoO and GaN, i.e., (111)_Co//(0001)_GaN and [11]_Co//[100]_GaN. Additionally, the atomic structures and electronic properties of the Co(111)/GaN(0001) interface are investigated by combining aberration-corrected scanning transmission electron microscopy and first-principles calculations. Utilizing Co/GaN as a model system, this study advances insights into the preparation of high-quality epitaxial metal/semiconductor heterojunctions.