In a method of forming a semiconductor device, a feature layer is provided on a substrate and a mask layer is provided on the feature layer. A portion of the mask layer is removed in a first region of the semiconductor device where fine features of the feature layer are to be located, the mask layer remaining in a second region of the semiconductor device where broad features of the feature layer are to be located. A mold mask pattern is provided on the feature layer in the first region and on the mask layer in the second region. A spacer layer is provided on the mold mask pattern in the first region and in the second region. An etching process is performed to etch the spacer layer so that spacers remain at sidewalls of pattern features of the mold mask pattern, and to etch the mask layer in the second region to provide mask layer patterns in the second region. The feature layer is etched using the mask layer patterns as an etch mask in the second region and using the spacers as an etch mask in the first region to provide a feature layer pattern having fine features in the first region and broad features in the second region.