Bias-dependent scanning tunneling microscopy (STM), used in conjunction with atomic-charge superposition calculations, is shown to provide information on both atomic and electronic surface structure. Si(111)-(7×7) STM images measured with different bias voltages are compared with a number of recent structural models. Striking agreement is found with the stacking-fault-adatom model of Takayanagi. The unit-cell asymmetry found at negative sample bias is attributed to a stacking fault in one half of the unit cell, locally modifying the surface electronic structure. © 1986 The American Physical Society.