A method includes forming an active pattern on a substrate, the active pattern comprising first semiconductor patterns and second semiconductor patterns, which are alternately stacked, forming a capping pattern on a top surface and a sidewall of the active pattern, performing a deposition process on the capping pattern to form an insulating layer, and forming a sacrificial gate pattern intersecting the active pattern on the insulating layer. The capping pattern has a crystalline structure and is in physical contact with sidewalls of the first semiconductor patterns and sidewalls of the second semiconductor patterns.