Abstract: A method for forming an element isolation insulating film of semiconductor devices, by which junction leakage current can be greatly reduced, comprising the steps of: forming a pad oxide film and a first insulating film on a semiconductor substrate, in sequence; patterning the pad oxide film and the first insulating film to expose an inactive region of the semiconductor device; constructing a spacer with a second insulating film at the side wall of the patterned first insulating film; etching the semiconductor substrate at a certain depth, to form a trench, the patterned first insulating film and the second insulating film spacer serving as a mask; implanting germanium impurities in the trench at a predetermined dose under a predetermined energy, to form an amorphous region to remove the lattice defective occurring upon forming the trench, the patterned first insulating film and the second insulating film spacer serving as a mask; crystallizing the amorphous region by a solid phase epitaxy process; and constr