A method of forming a contact structure includes forming an isolation region defining active regions in a semiconductor substrate. Gate patterns extending to the isolation region while crossing the active regions are formed. A sacrificial layer is formed on the semiconductor substrate having the gate patterns. Sacrificial patterns remaining on the active regions are formed by patterning the sacrificial layer. Molding patterns are formed on the isolation region. Contact holes exposing the active regions at both sides of the gate patterns are formed by etching the sacrificial patterns using the molding patterns and the gate patterns as an etching mask. Contact patterns respectively filling the contact holes are formed. The disclosed method of forming a contact structure may be used in fabricating a semiconductor device.