A composition for forming a silica layer includes a silicon-containing polymer and a solvent, the composition having a SiO2 conversion rate of greater than about 0 and less than or equal to about 15. The SiO2 conversion rate is represented by: SiO2 conversion rate=(a ratio of an area of Si—O to an area of Si—H measured after coating the composition in a thickness of 6700 Å on a bare wafer, and allowing the coated wafer to stand for 24 hours under conditions of a temperature of 85° C. and a relative humidity of 85%)−(a ratio of an area of Si—O to an area of Si—H measured after coating the composition in a thickness of 6700 Å on a bare wafer, and allowing the coated wafer to stand for 2 hours under conditions of a temperature of 85° C. and a relative humidity of 85%).