An object is to provide a technology capable of suppressing a crack of a crystalline nitride layer which is generated due to a stress caused by difference in thermal expansion coefficients between a crystalline nitride and diamond. A semiconductor device includes a crystalline nitride layer, a structure containing silicon, and a diamond layer. The structure is disposed on a first main surface of the crystalline nitride layer. The diamond layer is disposed at least on a lateral portion of the structure and has a void between the diamond layer and the first main surface of the crystalline nitride layer. The void is a stress absorbing space, for example.