A method of forming a semiconductor device having a contact structure includes forming an insulating layer on a semiconductor substrate, and selectively implanting impurity ions into a predetermined region of the insulating layer to generate lattice defects in the predetermined region of the insulating layer. A thermal treatment, such as quenching the insulating layer at a temperature change rate of at least −20° C./minute, is performed on the insulating layer having the lattice defects to accelerate generation of the lattice defects in the predetermined region such that a conductive region results from the generated lattice defects to provide current paths in the predetermined region.