A semiconductor device includes: a mounting board; and a semiconductor element disposed on the mounting board via metal bumps, wherein the semiconductor element includes a semiconductor stacked structure and first electrodes, the mounting board includes second electrodes, the metal bumps include a first layer in contact with the first electrodes of the semiconductor element and a second layer located on a side opposite to the first electrodes, an average crystal grain size of crystals included in the first layer is larger than an average crystal grain size of crystals included in the second layer, and the second layer is spaced apart from the first electrodes of the semiconductor element.