We present a technique for the fabrication of materials integration of (100) silicon and (100) gallium arsenide by direct wafer bonding. GaAs wafers 3 in. in diameter were hydrophobically bonded to commercially available 3 in. silicon-on-sapphire wafers at room temperature. After successive annealings in hydrogen and arsenic atmospheres at temperatures up to 850 °C the Si/GaAs interfacial energy was increased by the formation of strong covalent bonds. Due to the difference in the lattice constants of about 4.1&percent;, extra Si lattice planes were observed at the interface. No threading dislocations were introduced into the GaAs. ©1998 American Institute of Physics.