The photoluminescence spectra of type-I alignment Si/si(1-x)-(x)Ge(x)/Si heterostructures contained thin Si(1-x)Ge(x) layers (d=25-70 nm) are studied under various temperatures and excitation intensities. It was shown, excitation intensity increase at low temperatures leads to the exciton condensation resulting electron-hole liquid (EHL) formation in Si(1-x)Ge(x) layer. Electron-hole pair density no and binding energy of the EHL relative to exciton gas c decrease noticeably while x increases. The decrease in the binding energy and density of the electron-hole liquid is attributed to splitting of conduction and valance bands due to internal strains in the Si(1-x)Ge(x) layer. The Mott transition (from the exciton gas to electron-hole plasma) occurs above the critical temperatures for high excitation intensities. (c) 2008 Elsevier B.V. All rights reserved.