A compound for filling small gaps in a semiconductor device, a composition for filling small gaps in a semiconductor device, and a method of fabricating a semiconductor capacitor, the compound including hydrolysates prepared by hydrolysis, in the presence of an acid catalyst, of compounds represented by Formulae 1, 2, and 3: [RO]3Si—[CH2]nR′  (1) wherein, in Formula 1, n is an integer from 0 to about 10, and R and R′ are each independently a hydrogen atom, a C1-C12 alkyl group, or a C6-C20 aryl group; HOOC[CH2]nR2Si—O—SiR′2[CH2]nCOOH  (2) wherein, in Formula 2, each n is independently an integer from 0 to about 10, and R and R′ are each independently a C1-C12 alkyl group or a C6-C20 aryl group; and R3Si—O—X  (3) wherein, in Formula 3, X is R′ or SiR′3, and R and R′ are each independently a C1-C12 alkyl group or a C6-C20 aryl group, or a polycondensate prepared by polycondensation of the hydrolysates represented by Formulae 1, 2, and 3.