The atomic arrangements and the surface electronic states of a small amount of Si or Ge deposited on Si(001) were examined by scanning tunneling microscopy/scanning tunneling spectroscopy. Most of the deposited Si or Ge atoms were arranged as extended overlayer dimer rows, where some atoms occupied sites separated by a few surface lattice constants from the ends of the dimer rows. These sites can capture the deposited atoms migrating along the dimer rows of the substrate, indicating a possible difference of the surface electronic states between these sites and those of the substrate. The tunneling spectra on the sample surfaces showed the dependence on the separation between a tip and the surface.