Resin-encapsulated BGA semiconductor device package

An interconnect pattern 14 is formed on a metallic substrate by electrolytic plating, a chip 15 is mounted on and connected to the interconnect pattern, and after encapsualting the chip and the interconnect pattern with a mold compound 17, the metallic substrate is removed by etching. BGA electrodes are connected to the interconnect pattern via through-holes in an insulating film 19 formed over the interconnect pattern. The device package can be made thinner by grinding away the top surface of the encapsulation and the chip.