The authors report on the Raman scattering spectra and fundamental absorption edge of dense semiconductor-insulator nanocomposites. These were synthesized by injection of the semiconducting melt into the channels of dielectric matrices. The Raman spectra exhibit shifts, broadenings, and asymmetries consistent with phonon confinement in nanometre-size shifts, broadenings, and asymmetries consistent with phonon confinement in nanometre-size semiconductor crystallites. Nanoscale networks of small effective mass semiconductors show evidence for electron confinement as manifested by a blue shift of the fundamental absorption edge.