We present a scanning tunneling spectroscopy technique that allows one to make spatial maps of the characteristic length, i.e., the inverse decay length (), in electron tunneling. The method requires that the tunneling current i and its first and second derivative with distance di/dz and d2i/dz2, respectively, are simultaneously recorded. The derivatives di/dz and d2i/dz2 are recorded using a lock-in technique. A spatial map of provides valuable information on the electronic structure of surfaces, especially in case of semiconductors, nanostructured surfaces and molecules at surfaces. We have coined this spectroscopic technique microscopy.