Methods of forming patterns for semiconductor devices are provided. A method may include preparing a substrate including an etch target layer on a surface of the substrate; forming a mask pattern that includes a lower masking layer having a first density and an upper masking layer having a second density that is less than the first density, on the etch target layer; forming spacers that cover sidewalls of the lower masking layer and the upper masking layer; removing the mask pattern; and etching the etch target layer by using the spacers as an etching mask.