Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate were investigated by using the small-angle light scattering (SALS) and the small-angle neutron scattering (SANS). Under a fixed strain amplitude of oscillatory shear flow at 4.8, we observed the shear-induced structures as a function of the angular frequency (omega) and the strain-phase. At low w, butterfly patterns, which are the scattering patterns unique to the shear-induced structures formed in semidilute polymer solution, were observed by SALS and isotropic patterns with weak scattered intensities were obtained by SANS. At high omega, on the other hand, SANS showed butterfly patterns and SALS showed almost isotropic patterns. These results indicate that the anisotropic structures developed under oscillatory shear flow become smaller with increasing omega. From the SALS and SANS patterns, we obtained scattering profiles parallel and perpendicular to the flow direction. At omega higher than 0.6133 rad/s, the SANS profiles parallel to the flow direction could be reproduced by a linear combination of the squared Lorentzian (SQL) function, which reflects the scattering from the random two-phase structures, and the Ornstein-Zernike (OZ) function, which gives the scattering from concentration fluctuations in a single phase. This analysis suggests that the shear-induced structures are not just the concentration fluctuations in a single phase but kind of phase-separated structures having well-defined interfaces between two phases.