The dielectric function of Si nanocrystals embedded in a SiO2 matrix has been determined in the 1.6-6.2 eV spectral range. The Si nanocrystals have been obtained by annealing at 1000 degreesC SiOx layers with x = 1.1 and 1.9. The dielectric function of the Si clusters has been determined without the use of any dispersion model. It exhibited three critical points located at 3.5, 4.25 and 5.6 eV for x = 1.1 attributed to E-1, E-2 and E'(1), respectively For x = 1.9 the contribution of E-1 to the dielectric function intensity was strongly reduced while it increased at E-2. E'(1) was independent of x the composition of the films. (C) 2003 Elsevier B.V. All rights reserved.