Methods of manufacturing semiconductor devices

A method of manufacturing a semiconductor device, the method comprising:

• forming a plurality of preliminary gate structures on a substrate;
• forming a capping layer pattern on sidewalls of the plurality of preliminary gate structures and on a top surface of the substrate between the preliminary gate structures;
• forming a blocking layer on top surfaces of the plurality of preliminary gate structures and the capping layer pattern such that a void is formed between the blocking layer and the capping layer pattern;
• removing the blocking layer and an upper portion of the capping layer pattern such that at least the upper sidewalls of the plurality of preliminary gate structures are exposed, a lower portion of the capping layer pattern remaining on lower sidewalls of the preliminary gate structures;
• forming a conductive layer on at least the upper sidewalls of the plurality of preliminary gate structures;
• reacting the conductive layer with the preliminary gate structures to form a plurality of gate structures;
• and
• forming a second insulation layer on the substrate to cover the gate structures, the second insulation layer having an air gap therein between the plurality of gate structures.