Optical and electrical properties of single-crystal Si supersaturated with Se by ion implantation and followed by different thermal annealing conditions are reported.Si is implanted with 1 × 1016 cm-2 Se ions at 100keV.The total substitutional fraction of Se atoms in Si is 45％ under the annealing at 800℃ for 30min and the peak concentration of substitutional Se atoms is exceeded 1 × 1020 cm-3.A temperature-independent carrier concentration of 3 × 1019 cm-3 is measured and the near-infrared absorption is closed to 30％.These results indicate the insulator-to-metal transition of the doped layer and the formation of impurity bands in the Si band gap.