A semiconductor device includes a semiconductor layer and a metal electrode. The metal electrode is provided on the semiconductor layer. The metal electrode includes first to third metal regions. The first metal region contacts the semiconductor layer and includes a first metal element as a main component. The second metal region is provided on the first metal region and includes a second metal element as a main component. The third metal region is provided on the second metal region. The third metal region has a thickness in a first direction directed from the semiconductor layer toward the second metal region. The thickness of the third metal region is larger than a total thickness in the first direction of the first metal region and the second metal region. The second metal element has a standard free energy of oxide generation larger than that of the first metal element.