Surface imperfections of silicon‐on‐insulator (SOI) wafers are investigated by means of extremely asymmetric x‐ray reflection topography, in which the glancing angle of the incident x rays is near the critical angle of total reflection; this geometry is achieved by using tunable wavelength synchrotron radiation. Two kinds of SOI wafers: bonded and two oxygen implanted silicon wafers are used as samples. The experimental topographs reveal a characteristic contrast for each sample, which cannot be observed by conventional x‐ray topography. The observed contrasts strongly depend on the fabrication techniques of the SOI wafers. ©1996 American Institute of Physics.