The present invention provides a method for forming insulating film between interconnect layers in microelectronic devices, said method comprising the steps of: preparing siloxane-based resins by hydrolyzing and polycondensing the compound represented by the following formula (1), with or without the compound represented by the following formula (2), in an organic solvent in the presence of a catalyst and water; coating a silicon substrate with the siloxane-based resins dissolved in an organic solvent; and heat-curing the resulting coating film:  RSiX1X2X3  [2] in which, R is hydrogen atom, C1˜C3 alkyl group, C3˜C10 cycloalkyl group, or C6˜C15 aryl group; X1, X2 and X3 are independently C1˜C3 alkyl group, C1˜C10 alkoxy group, or halogen atom; n is an integer ranging from 3 to 8; and m is an integer ranging from 1 to 10.