  Electronic properties of the Si(111)-$7\times 7$ surface are studied using
four- and two-probe conductivity measurements and tunneling spectroscopy. We
demonstrate that the temperature dependence of the surface conductivity
corresponds to the Efros-Shklovskii law at least in $10-100$~K temperature
range. The energy gap at the Fermi level observed in tunneling spectroscopy
measurements at $T\geq 5$~K vanishes by thermal fluctuations at $T\approx
30$~K, without any sign of the metal-insulator transition. We show that the
low-temperature energy gap observed by the tunneling spectroscopy technique is
actually the consequence of the Coulomb blockade effect.
