a wafer of semiconductor material for fabricating integrated devices , including a stack of superimposed layers including first and second monocrystalline silicon layers separated by an intermediate insulating layer made of a material selected from the group comprising silicon carbide , silicon nitride and ceramic materials . an oxide bond layer is provided between the intermediate layer and the second silicon layer . the wafer is fabricated by forming the intermediate insulating layer on the first silicon layer in a heated vacuum chamber ; depositing the oxide layer ; and superimposing the second silicon layer . when the stack of silicon , insulating material , oxide and silicon layers is heat treated , the oxide reacts so as to bond the insulating layer to the second silicon layer . as a ceramic material beryllium oxide , aluminium nitride , boron nitride and alumina may be used .