In situ Hall measurements of submonolayer and monolayer Si(111)/Fe, Si(111)/Cr and Si(111)/Mg disordered systems are presented. It was shown that for understanding conductivity mechanism in a system adsorbed metal (Fe, Cr, Mg)/Si(111) 7 x 7, it is necessary to take into account three effects: (af destruction of the superstructure Si(111) 7 x 7: (b) formation of donor-type surface states of Fe (Cr) in the band gap of silicon and (c) growth mode of the silicide or metal (Mg) clusters on Si surface. Destruction of the localized surface states of superstructure Si(111) 7 x 7 plays the greatest role, if the density of donor-type surface states is very small. It corresponds to adsorption of Cr and Mg on Si(111) of p-type. The greatest contribution of donor-type surface states to the conductivity of surface space-charge layer is observed with adsorption of Fe on Si(111) of n-type. Conductivity through the adsorbed iron (chromium) layer begins with thickness more than three monolayers and is supported by electrons.