First-principle calculations are performed to explore the energetics and electronic structures of semiconducting nanotubes adsorbed on the (0001) surfaces of alpha-quartz (SiO2). We find that the absorption energy of nanotube on SiO2 is similar to 0.4 eV/nm, strongly depends on the adsorption site and the inter-unit spacing of the nanotube and the SiO2. The electronic structure of this hybrid structure is semiconducting so that the electronic states near the energy gap are caused by those of the nanotubes. A detailed analysis of the electron states of the nanotubes reveals that the energy gaps between valence and conduction bands are slightly modulated by adsorption. (C) 2009 Elsevier B.V. All rights reserved.