A bonding structure of a ball-bonded portion is obtained by bonding a ball portion formed on a front end of a multilayer copper bonding wire. The multilayer copper bonding wire includes a core member that is mainly composed of copper, and an outer layer that is formed on the core member and is mainly composed of at least one noble metal selected from a group of Pd, Au, Ag and Pt. Further, a first concentrated portion of such noble metal(s) is formed in a ball-root region located at a boundary with the copper bonding wire in a surface region of the ball-bonded portion.