Methods are provided for manufacturing semiconductor devices include forming a first fin protruding on a substrate and extending in a first direction; forming first and second sacrificial gate insulating layers on the first fin, the first and second sacrificial gate insulating layers intersecting the first fin and being spaced apart from each other; forming first and second sacrificial gate electrodes respectively on the first and second sacrificial gate insulating layers; forming a first insulating layer on the first and second sacrificial gate electrodes; removing a portion of the first insulating layer to expose the second sacrificial gate electrode; removing the exposed second sacrificial gate electrode using a first etching process to expose the second sacrificial gate insulating layer; removing the exposed second sacrificial gate insulating layer using a second etching process different from the first etching process to form a first trench which exposes the first fin; forming a first recess in the exposed first fin using a third etching process different from the second etching process; and filling the first recess with a first device isolation layer.