Methods of manufacturing semiconductor devices

A method of manufacturing a semiconductor device, comprising:

• forming mask patterns on a semiconductor substrate;
• forming an organic layer on the semiconductor substrate to cover the mask patterns;
• planarizing an upper portion of the organic layer using a polishing composition, the polishing composition including an oxidizing agent and being devoid of abrasive particles;
• forming an object layer on the semiconductor substrate before forming the mask patterns, wherein forming the mask patterns includes forming first organic layer patterns on the object layer and forming spacers on sidewalls of the first organic layer patterns, wherein the organic layer fills spaces between the spacers and planarizing the upper portion of the organic layer includes forming second organic layer patterns between the spacers;
• removing the spacers after forming the second organic layer patterns to form openings;
• and
• etching the object layer through the openings.