A nonvolatile memory device and a method of forming the nonvolatile memory device, the method including forming a tunnel insulating layer on a substrate, wherein forming the tunnel insulating layer includes forming a multi-element insulating layer by a process including sequentially supplying a first element source, a second element source, and a third element source to the substrate, forming a charge storage layer on the tunnel insulating layer, forming a blocking insulating layer on the charge storage layer, and forming a control gate electrode on the blocking insulating layer.