The structures of GaAs/Ge/GaAs(001) crystals designed for prototypes of nonlinear optical devices were investigated by X-ray diffraction (XRD). The intensity distribution of crystal truncation rod (CTR) scattering showed that the quality of GaAs epitaxial layers is good. The results of X-ray standing wave (XSW) measurements clearly indicated that the 90 degrees rotation of the epitaxial layers, which is a necessary condition for the phase matching, occurs.