Abstract: The mechanism and potential energy surface of ［2 + 2］, ［4 + 2］ and ［4 + 4］ dimerization reactions of some tricyclic silaaromatic compounds (1silaanthracene, 2silaanthracene and 9silaphenanthrene) were studied by using density functional theory (DFT) at the B3LYP/631G* level. The obtained results were compared with those of dimerization reactions of silabenzene, 1silanaphthalene and 2silanaphthalene studied previously. The results showed that ［2 + 2］ and ［4 + 4］ reactions occur in a concerted and synchronous way, while ［4 + 2］ reactions proceed in a concerted but nonsynchronous way. ［2 + 2］ and ［4 + 2］ Reactions of 1-silaanthracene proceed much more easily than corresponding ［4 + 4］ reactions both thermodynamically and kinetically. The difference between exo and endo approaches is not obvious both in the thermodynamic and kinetic properties. 1-Silaanthracene (2-silaanthracene) has higher reactivity and hence lower stability than silabenzene and 1-silanaphthalene (2-silanaphthalene).