Field effect-scanning electron microscopy (FE-SEM) and electric force microscopy (EFM) measurements were carried out on bulk Ag2S-As2S3 glasses with silver concentrations 1.2, 4 and 9.8 at.%. While the first glass was found to be homogeneous, the presence of chemical contrasts and electrical heterogeneousness throughout the other two samples indicated that the glasses were phase separated. Moreover, it appeared that, while silver-rich nodules of 200-350 nm were embedded in a silver-poor connecting phase in the glass containing 4 at.% Ag, it was the opposite that occurred in the glass containing 9.8 at.% Ag. Such an inversion explained the large difference of 4-5 orders of magnitude in the conductivity of the two glasses. (c) 2006 Elsevier B.V. All rights reserved.