PURPOSE: To produce the Cu alloy provided with conductivity, strength, radiating capacity and heat resistance required for the lead wire of highly integrated semiconductor device by a method wherein specified amount of Sn, P and Fe are added to Cu alloy.

CONSTITUTION: A lead wire is made of Cu alloy comprising Sn, P and Fe respectively amounting to 1.5W4.5%, 0.01W0.05% and 0.05W0,15% as well as the residual Cu and indispensable impurities. Such a Cu alloy is optimum for the lead wire of highly integrated semiconductor device since it is provided with the properties such as tensile strength exceeding 55kgf/mm2, Vickers' hardness exceeding 170, elongation exceeding 3%, conductivity exceeding 20% IACS, softening point exceeding 400°C. The Sn content in the composition of said Cu alloy may improve the strength of lead wire remarkably while P and Fe may improve the heat resistance since they disperse and separate themselves as ferrous phosphide finely and evenly in the base metal during the cold rolling operation in the raw material production process of the lead wire.