A nitride semiconductor device includes a silicon substrate, a nitride semiconductor layer formed on the silicon substrate, and metal electrodes formed in contact with the silicon substrate. The metal electrodes has first metal layers which are formed in a shape of discrete islands and in contact with the silicon substrate, and second metal layers which are in contact with the silicon substrate exposed among the islands of the first metal layers and are formed to cover the first metal layers. Further, the second metal layers are made of a metal capable of forming ohmic contact with silicon, and the first metal layers are made of an alloy containing a metal and silicon, in which the metal is different than that in the second metal layer.