A combined scanning tunneling microscopy/scanning tunneling spectroscopy (STS) system has been developed by which the spatially resolved electronic structure of a surface can be measured step by step consecutively. With this system, etched GaAs(100) surfaces have been studied in ambient with experimental measurements of the (d ln I/d ln V) vs V curves along a line on the surfaces. The curves exhibit the basic band structure of GaAs. Specific band energies from the curves are plotted versus the surface position at which each of the corresponding STS spectra is measured. The plots show a correlative variation of the surface electronic structure with the surface corrugation. The results present the possibility of investigating the spatial variation of the surface electronic states with surface structures. Based on the correlative variation of the surface electronic structure, a way of imaging the surface corrugation more sensitively is proposed.