In a method of forming patterns of a semiconductor device, a semiconductor substrate defining photoresist patterns formed over a target etch layer is provided. An auxiliary layer is formed over the semiconductor substrate and the photoresist patterns. The auxiliary layer formed on a surface of the photoresist patterns is denatured into first auxiliary patterns. A photoresist film is formed over the semiconductor substrate, the first auxiliary patterns, and the auxiliary layer. The auxiliary layer formed below the photoresist film is denatured into a second auxiliary pattern. Here, the auxiliary layer remains only between the photoresist patterns. Etch mask patterns, including the photoresist patterns and the auxiliary layer, are formed by removing the photoresist film and the first and second auxiliary patterns.