In a method or joint for joining first and second semiconductor wires, each comprising a number of filaments which each comprise a superconductive core within a respective sheath, the filaments being embedded within a matrix and wherein the superconductive cores comprise magnesium diboride and the sheaths comprise niobium, over a certain length a matrix is removed to expose the filaments. The exposed filaments are immersed in molten tin such that the nobium of the sheaths is converted to niobium-tin throughout a thickness of the sheaths. A superconductive path is provided between the superconductive cores of filaments of the first wire through the niobium-tin sheaths of the filaments to the superconductive cores of the second wire.