Results of white beam X-ray interference measurements on almost perfect semiconductor wafers are presented. A specific measurement geometry allows for the investigation of diffraction effects on thin wafers down to at least 375 µm with a simple experimental setup (standard lab CT with microfocus X-ray tube). Furthermore, the dynamic diffraction effect of double refraction has been studied in detail for thicker samples. This might lead to a new wafer testing method as the observed dynamic effects are very sensible on crystal quality.