In a method, an isolation layer pattern is formed on a substrate to define first and second active fins. An ARC layer is formed on the isolation layer pattern to at least partially cover sidewalls of the first and second active fins. A level of a top surface of the ARC layer is equal to or less than, and equal to or greater than half of, those of the first and second active fins. A photoresist layer is formed on the first and second active fins and the ARC layer. A portion of the photoresist layer is removed to form a photoresist pattern covering the first active fin and exposing the second active fin. A portion of the ARC layer under the removed portion of the photoresist layer is removed to form an ARC layer pattern. Impurities are implanted into the exposed second active fin to form an impurity region.