The state-selective positive-ion and negative-ion dissociation pathways for gaseous and condensed Si(CH 3) 2Cl 2 following the Cl 2p and Si 2p core-level excitations have been characterized using synchrotron radiation. The Si 2p→15a1∗ excitation of Si(CH 3) 2Cl 2 induces an enhancement of the Cl + desorption yield in the condensed phase and the Si(CH3)2+ and SiCH3+ yields in the gaseous-phase. The Cl -desorption yields are notably enhanced at the 15a1∗ resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl - yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide an insight into the comprehensive understanding of the state-selective fragmentation of molecules via core-level excitation.