Surface structure and electrical conductance of the (Au,Ag)/Si(11 1) two-dimensional system have been studied in situ with low-energy electron diffraction, scanning tunneling microscopy and four-point probe technique. The new surface structure identified as Si(1 1 1)root 93 x root 93-(Au, Ag) has been found to form upon deposition of similar to 0.1 ML of Ag onto Si(1 1 1)alpha-root 3 x root 3-Au surface held at 350 degrees C. With further Ag deposition at this growth temperature, the surface structure evolves to Si(1 1 1)2 root 3 x 2 root 3 and eventually to Si(1 1 1)root 21 x root 21. Structural transformations have been found to be accompanied by non-monotonous changeover of the surface conductance. Possible factors affecting the surface conductivity are discussed. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.