In order to fabricate atomically controlled organic materials on Si surfaces, the electronic states of unsaturated cyclic cyclic hydrocarbons chemisorbed on Si(1 0 0)(2 x 1) surfaces were investigated by synchrotron radiation ultraviolet photoelectron spectroscopy (UPS) as a fundamental study. For cyclopentene and cyclohexene, the C=C bond interacts with the Si dimer, resulting in the formation of di-sigma Si-C bonds. In the case of 1,4-cyclohexadiene, on the other hand, one of two C=C bonds reacts with the Si dimer and another C=C bond remains unreacted with the Si surface. This intact C=C bond may introduce the possibility of subsequent functionalization of the organic film, and for the fabrication of atomically controlled and highly functional organic film/Si devices.