A semiconductor structure includes a substrate, a first nitride layer, a second nitride layer, a third nitride layer, and a polarity inversion layer. The first nitride layer is formed on the substrate, and the polarity inversion layer formed at a surface of the first nitride layer converts a non-metallic polar surface of the first nitride layer into a metallic polar surface of the polarity inversion layer. The second nitride layer is formed on the polarity inversion layer. The third nitride layer is formed on the second nitride layer.