Method for fabricating semiconductor device

A method for fabricating a semiconductor device having a GaN-based semiconductor layer on a first surface of a substrate made of SiC, a pad being provided on the GaN-based layer, comprising:

• forming a first via hole in the substrate by etching, with fluorine based gas, from a second surface of the substrate opposite to the first surface, the etching being carried out with the GaN-based layer being used as an etch stopper;
• and
• forming a second via hole in the GaN-based semiconductor layer, with chlorine based gas, from a bottom surface of the first via hole, the etching being carried out with the pad being used as an etching stopper, the chlorine based gas being an etchant different from the fluorine based gas,
• wherein the forming of the first via hole includes etching with a mask layer that is formed on the second surface of the substrate, and the mask includes any of Cu, Ni and Pt, and the forming of the second via hole is carried out by etching with the substrate being used as a mask;
• removing the mask used in the forming of the first via hole before carrying out the forming of the second via hole.