A semiconductor device has a first semiconductor pellet and a second semiconductor pellet. An electrode-forming surface of the first semiconductor pellet on which flat electrodes having flat surfaces are formed and an electrode-forming surface of the second semiconductor pellet on which protruded electrodes are opposed to each other. Also, the flat electrodes and the protruded electrodes are electrically connected to each other. A main component of a conductive material that forms the flat electrode is the same as a main component of a conductive material that forms the protruded electrode. Furthermore, the hardness of the protruded electrode is higher than the hardness of the flat electrode. Therefore, the protruded electrodes and the flat electrodes can be electrically connected to each other with high reliability.