Perovskite oxide semiconductors have attracted a great deal of attention as new device materials because they show multifunctional properties beyond those of conventional semiconductors. With its unique electrical and optical properties, SrTiO3 is a key material in oxide electronics. In this chapter, we discuss the optical properties and carrier recombination dynamics of SrTiO3 bulk crystals. Electrondoped and strongly photoexcited SrTiO3 crystals show photoluminescence (PL) consisting of three components: a 2.5-eV green PL, a 2.9-eV blue PL, and a 3.2-eV band-to-band PL. The blue PL dynamics in the presence of high-density carriers is determined by nonradiative three-carrier Auger recombination. The PL spectra and dynamics of undoped SrTiO3 under strong photoexcitation are very similar to those of electron-doped SrTiO3. From the PL decay dynamics, we evaluate the electron density in the near-surface oxygen-deficient region in SrTiO3 bulk crystals and nanoparticles. PL spectra of other d0-type perovskite semiconductors, KTaO3, BaTiO3, LiNbO3, and LiTaO3, are also discussed in comparison with SrTiO3.