To obtain a lead frame which is improved in dimensional accuracy, lessened in number of post-treatments, and improved in structure so as to enable a device product to be lessened in thickness.

A hoop material is formed by being pressed into a lead frame 1, which is used for assembling a semiconductor device. The lead frame 1 is composed of a mount 1a, where a semiconductor chip 2 is mounted, a mount 1c where a control circuit board 3 is mounted, and outer leads 1b which are formed by patterning, where the mount 1c is pressed down from above the mount 1a and the outer leads 1b so as to be recessed, the outer leads 1b are not subjected to bending work, and wires 4 are each bonded to the outer leads 1b respectively. Moreover, a hoop material used for fabricating a lead frame is formed by rolling to enable the thicknesses of its regions corresponding to a mount 1a, an outer lead 1b, and a mount 1c are set to the relations, t1>t3>t2, where t1, t2, and t3 denote the thiecnknesses of the mount 1a, lead 1b, and mount 1c.