We summarized our recent optical studies on perovskite semiconductor SrTiO3 crystals. Photocarrier recombination dynamics of undoped, electron-doped, and vacancy-doped SrTiO3 crystals were studied by photoluminescence (PL) and transient absorption (TA) spectroscopy. By high-density photoexcitation and electron doping, the blue PL is clearly observed in SrTiO3 crystals at room temperature. The PL spectrum and dynamics are sensitive to the photoexcited carrier density and the chemically doped electron density. The PL and TA decay dynamics under high-density excitation are determined by nonradiative Auger recombination. It is demonstrated that the PL lifetime can be used as a probe for determining spatial profiles of carriers and defects in SrTiO3.