Remarkably low electron density of Si adatoms at the Si(111)‐7×7 phase boundary was found by scanning tunneling microscopy. The observed charge transfer was apparent with sample bias voltages down to ∼−0.8 eV, close to the value of the dangling bond state of the rest atoms in the Si(111) 7×7 surface. In consideration of the DAS (dimer‐adatom‐stacking fault) model, the observed charge transfer could be related to the structural change in the dimer layer caused by phase mismatching at the boundary. In fact, such charge transfer was not observed at the less disordered boundaries formed by introducing 5×5 half unit cells. Similar large charge transfer was found to occur in the quenched disordered 1×1 structure. These results agree with the similar chemical reactivity observed in the two disordered structures. ©1995 American Institute of Physics.