This invention provides a Cu-Mn alloy sputtering target characterized by comprising 0.05 to 20% by weight of Mn and not more than 500 ppm by weight in total of Be, B, Mg, Al, Si, Ca, Ba, La, and Ce with the balance consisting of Cu and unavoidable impurities. There is also provided a copper alloy wiring for a semiconductor, wherein a self-diffusion suppression function can be imparted to the copper alloy wiring for a semiconductor per se to effectively prevent contamination of a part around the wiring by the diffusion of active Cu. Further, in the copper alloy wiring for a semiconductor, for example, electromigration (EM) resistance and corrosion resistance have been improved, a barrier layer can be arbitrarily and easily formed, and, further, the film forming step of a copper alloy wiring for a semiconductor can be simplified. A sputtering target for the formation of the wiring, and a method for forming a copper alloy wiring for a semiconductor are also provided.