Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device, comprising:

• preparing a semiconductor substrate including a first semiconductor layer and a second semiconductor layer disposed on the first semiconductor layer, the first semiconductor layer made of gallium oxide containing Sn, the second semiconductor layer made of n type gallium oxide having a Sn concentration lower than a Sn concentration of the first semiconductor layer;
• implanting ions of a group 2 element into the second semiconductor layer;
• and
• forming a diffusion region, in which the group 2 element diffuses, in a range from a surface of the second semiconductor layer to an interface between the second semiconductor layer and the first semiconductor layer.