String floating gates with air gaps in between

A semiconductor device comprising:

• a plurality of strings spaced apart a first distance from each other on a substrate,
• each string including a plurality of second gate structures and a plurality of first gate structures, the first gate structures being between innermost ones of the second gate structures,
• the first gate structures being spaced apart from each other a second distance less than the first distance, and
• outermost ones of the first gate structures being spaced apart from the innermost ones of the second gate structures a third distance less than the first distance
• a first insulation layer pattern only on a lower portion of outer sidewalls of outermost ones of the second gate structures in each string and portions of the substrate adjacent to the outer sidewalls of the outermost ones of the second gate structures;
• a spacer structure on the first insulation layer pattern;
• and
• a capping layer on the first and second gate structures, the first insulation layer pattern and the spacer structure, the capping layer defining air gaps at least between the first gate structures, between the second gate structures, or between the outermost ones of the first gate structures and the innermost ones of the second gate structures, respectively.