PURPOSE: To reduce the cost of a semiconductor device substrate and to facilitate an easy alteration of its pattern by forming sprocket holes and a hole for containing a semiconductor element using a flexible insulating film, forming lead wires and an insulating foil, and working a pattern.

CONSTITUTION: Sprocket holes 12 are perforated at a flexible insulating film 11, and a hole 13 is also perforated at the portion for disposing a semiconductor element and lead wires. Then, a Cu lead wire 14 is formed on the film 11, and an insulating foil 15 formed with a hole 16 at the center is then formed from the back surface of the film 11 onto the lead wire 14. Subsequently, lead wires 17a, 17b are so formed as to bridge between the film 1 and the foil 15 at the film 14 to thus complete the production of the substrate.