A semiconductor device includes a substrate divided into a memory cell region and a logic region. A split gate electrode structure is formed in a memory cell region of a substrate. A silicon oxide layer is formed on a sidewall of the split gate electrode structure and a surface of the substrate. A word line is formed on the silicon oxide layer that is positioned on the sidewall of the split gate electrode structure. The word line has an upper width and a lower width. The lower width is greater than the upper width. A logic gate pattern is formed on a logic region of the substrate. The logic gate pattern has a thickness thinner than the lower width of the word line.