A method for fabricating interconnecting lines inside via holes of a semiconductor device comprises steps of providing a template having a receiving trench and a connection surface both on the same side of the template; filling an electric-conduction material into the receiving trench; connecting a substrate having at least one via hole with the connection surface to interconnect the via hole with the receiving trench; heating the electric-conduction material to a working temperature to liquefy a portion of the electric-conduction material and make it flows from the receiving trench into the via hole; and cooling the electric-conduction material to form an interconnecting line inside the via hole. The present invention fabricates interconnecting lines by a heat-forming method, which features simple steps and has advantages of shorter fabrication time, lower fabrication complexity, higher fabrication efficiency, higher yield and lower fabrication cost.