The atomic structure and charge transfer on the Ge (105) surface formed on Si substrates are studied using scanning tunneling microscopy and spectroscopy (STM and STS). The bias-dependent STM images of the whole Ge (105) facets formed on a Ge "hut" structure on Si (001) are observed, which are well explained by the recently confirmed structure model. The local surface density of states on the Ge (105) surface is measured by STS. The localization of the electronic states expected from charge transfer mechanism is observed in the dI/dV spectra. The surface band gap is estimated as 0.8-0.9 eV, which is even wider than the bulk bandgap of Ge, indicating the strong charge transfer effect to make the dangling bonds stable. The shape of normalized tunnel conductance agrees with the theoretical band structure published recently by Hashimoto et al. (c) 2005 Elsevier B.V. All rights reserved.