A nonvolatile memory device includes a substrate, an elongate isolation region including a field insulation film disposed in a trench in the substrate, and a word line crossing the insulation region and including a tunneling insulation layer on an active region of the substrate adjacent the isolation region, a charge storage layer on the tunneling insulation layer and a blocking insulation layer on the charge storage layer. A first plane index of a bottom surface of the trench has a first interface trap density and a second plane index of a sidewall of the trench has a second interface trap density equal to or less than the first interface trap density. In some embodiments, the first plane index may be (100) and the second plane index may be (100) or (310).