Directly bonded Si(011)/Si(001) substrates were prepared by conventional bonding and grind back methods. The bonding interface structure and crystallinity in the bonded substrate were studied by transmission electron microscopy and X-ray diffraction (XRD). The regular array of dislocations and the undulation were formed in the interface. From XRD analysis, it was confirmed that the crystallinity of the Si(011) layer in the bonded substrate deteriorated in comparison with the bulk Si(011) wafer. We proposed that directly bonded Si substrates with different crystal orientations induced stress at the bonding interface due to misfit bonding, as a result, the Si(011) layer was strained and the undulation was formed at the bonding interface. (c) 2008 Elsevier B.V. All rights reserved.