A nitride semiconductor device according to the present invention includes a n-GaN substrate 10 and a semiconductor multilayer structure arranged on the principal surface of the n-GaN substrate 10 and including a p-type region, an n-type region and an active layer between them. An SiO2 layer 30 with an opening and a p-side electrode, which makes contact with a portion of the p-type region of the semiconductor multilayer structure, are arranged on the upper surface of the semiconductor multilayer structure. An n-side electrode 36 is arranged on the back surface of the substrate 10. The p-side electrode includes a p-side contact electrode 32 that contacts with the portion of the p-type region and a p-side interconnect electrode 34 that covers the p-side contact electrode 2 and the SiO2 layer 30. Part of the p-side contact electrode 32 is exposed under the p-side interconnect electrode 34.