A nonvolatile memory device includes a semiconductor substrate, a tunneling insulation layer on the semiconductor substrate, a charge storage layer on the tunneling insulation layer, an inter-electrode insulation layer on the charge storage layer, and a control gate electrode on the inter-electrode insulation layer. The inter-electrode insulation layer includes a high-k dielectric layer having a dielectric constant greater than that of a silicon nitride, and an interfacial layer between the charge storage layer and the high-k dielectric layer. The interfacial layer includes a silicon oxynitride layer.