Provided is a method of forming patterns for a semiconductor device in which fine patterns and large-width patterns are formed simultaneously and adjacent to each other. In the method, a first layer is formed on a substrate so as to cover a first region and a second region which are included in the substrate. Both a blocking pattern covering a portion of the first layer in the first region and a low-density large-width pattern covering a portion of the first layer in the second region are simultaneously formed. A plurality of sacrificial mask patterns are formed on the first layer and the blocking pattern in the first region. A plurality of spacers covering exposed sidewalls of the plurality of sacrificial mask patterns are formed. The plurality of sacrificial mask patterns are removed. The first layer in the first and second regions are simultaneously etched by using the plurality of spacers and the blocking pattern as etch masks in the first region and using the low-density large-width pattern as an etch mask in the second region.