In a method of manufacturing a transistor and a method of manufacturing a semiconductor device using the same, the method may include forming a preliminary metal silicide pattern on a single-crystalline silicon substrate and on a polysilicon pattern, and partially etching the preliminary metal silicide pattern to form a first metal silicide pattern on the substrate and a second metal silicide pattern on the polysilicon pattern, the second metal silicide pattern having a line width the same as or smaller than that of the polysilicon pattern. The method may include the transistor having no metal silicide residue on the spacer. Accordingly, an operation failure due to the residue may be prevented or reduced.