There is provided a bump structure for a semiconductor device, comprising a first metal layer, and a second metal layer electrically connected to the first metal layer so as to be integrally formed with the first metal layer, and electrically connected to electrode pads of the semi¬ conductor device, in which the second metal layer is composed of one or more metals or alloys having the melting point higher than the melting point of the first metal layer or the eutectic temperature of the first metal layer and another substance when the first metal layer makes a fusion reaction to the surface of the another substance. Preferably, the second metal layer may have a thickness greater than that of the first metal layer. The bump structure may further comprise a diffusion prevention layer between the first metal layer and the second metal layer.