A nonvolatile memory device includes an upper insulating layer. A first substrate is on the upper insulating layer. An upper interlayer insulating layer is on the first substrate. A plurality of word lines is stacked on the first substrate in a first direction and extends through a partial portion of the upper interlayer insulating layer. A lower interlayer insulating layer is on the upper interlayer insulating layer. A second substrate is on the lower interlayer insulating layer. A lower insulating layer is on the second substrate. A dummy pattern is composed of dummy material. The dummy pattern is disposed in a trench formed in at least one of the first and second substrates. The trench is formed on at least one of a surface where the upper insulating layer meets the first substrate, and a surface where the lower insulating layer meets the second substrate.