Example embodiments relate to a method of forming a recess and a method of manufacturing a semiconductor device having the same. The method includes forming a field region defining an active region in a substrate. The active region extends in a first direction in the substrate. The method further includes forming a preliminary recess extending in a second direction different from the first direction and crossing the active region in the substrate, plasma-oxidizing the substrate to form a sacrificial oxide layer along a surface of the substrate having the preliminary recess, and removing portions of the sacrificial oxide layer and the active region by plasma etching to form a recess having a width larger than a width of the preliminary recess, where an etch rate of the active region is one to two times greater than an etch rate of the sacrificial oxide layer.