The synthesis and characterization of new hyperbranched organosilicon polymers containing furan or thiophene are described. The air- and moisture-stable polymers were prepared in 78-98% yields by the platinum-catalyzed hydrosilylation polymerization of AB(2) and AB(3) silyl-substituted furans and thiophenes. Complete polymerization was achieved within several hours at room temperature. Number-average molecular weights of the products ranged from similar to2000 to 4000, as determined by both gel permeation chromatography and vapor pressure osmometry. The polymers were highly soluble in common solvents and possessed glass transition temperatures well below room temperature. Si-29 NMR spectroscopy confirmed the branched nature of the polymers.