A process for manufacturing a metal plane support for making multi-layer lead frames adapted to be used for semiconductor devices. The lead frame support is made of a single thin metal strip having a plurality of lead frames continuously arranged in the longitudinal direction, the metal plane support is also made of a single thin metal strip and includes a plurality of metal planes, such as power supply planes, ground planes of the like, continuously arranged in the longitudinal direction corresponding to said plurality of lead frames. A pair of side rails are extending in the longitudinal direction for supporting the metal planes therebetween. The metal planes are connected to the rails via separating portions for removing the rails from the metal planes, after the metal planes are adhered to the corresponding lead frames.