A semiconductor device having a structure in which a semiconductor element and a Cu or Ni electrode are connected by way of a bonding layer comprising Cu, and the Cu bonding layer and the Cu or Ni electrode are diffusion-bonded to each other. The bonding layer is formed by conducting bonding in a reducing atmosphere by using a bonding material containing particles of Cu oxide with an average particle size of 1 nm to 50 μm and a reducing agent comprising an organic material, thereby providing excellent bonding strength to Ni or Cu electrode.