Oxide semiconductor SrTiO_3 single crystals are exposed to a reducing atmosphere H_2/N_2 to induce the reduction of Ti~(4+) to Ti~(3+) and the release of oxygen from the lattice compensating the reduction of the Ti ions.In a reducing atmosphere H_2/N_2 the optical edge brings about a red shift.The infrared reflection spectra suggest that the(11) STO single crystal surface can be terminated by the domain of the SrO or TiO_2 alternative layer during the reduction.The anisotropy and asymmetry of optical second-harmonic intensity explain a slight shrinkage.The dielectric constant reaches about 6000 and shows almost frequency dependence at all temperatures.With the increasing temperature,the dielectric constant increases rapidly.The high temperature region and low temperature region have activation energies of 0.89 and 1.04,respectively. Oxide semiconductor SrTiO 3 single crystals are exposed to a reducing atmosphere H 2 / N 2 to induce the reduction of Ti ~ (4+) to Ti ~ (3+) and the release of oxygen from the lattice compensating the reduction of the Ti ions. A reducing atmosphere H 2 / N 2 the optical edge brings about a red shift. The infrared reflection spectra suggest that the (11) STO single crystal surface can be terminated by the domain of the SrO or TiO 2 alternative layer during the reduction. anisotropy and asymmetry of optical second-harmonic intensity explain a slight shrinkage. The dielectric constant reaches about 6000 and shows almost frequency dependence at all temperatures. At the increasing temperature, the dielectric constant increases rapidly. the high temperature region and low temperature region have the activation energies of 0.89 and 1.04, respectively.