The electronic states of the Cl-chemisorbed Si(111) surface and the basic characteristics of laser-induced surface reaction of the Si(111)/Cl system have been studied using second-harmonic generation (SHG). The SHG spectrum from the Cl-chemisorbed Si(111) surface showed resonance peaks involving the chlorine-induced electronic states at 1.6 and 2 eV. The laser-induced surface reaction of the Si(111)/Cl system was strongly affected by the interference between the pump and probe beams.