A method for manufacturing a gallium nitride (GaN) wafer is provided. In the method for manufacturing the GaN wafer according to an embodiment, an etch stop layer is formed on a substrate, and a first GaN layer is formed on the etch stop layer. A portion of the first GaN layer is etched with a silane gas, and a second GaN layer is formed on the etched first GaN layer. A third GaN layer is formed on the second GaN layer.