The quality of ELTRAN wafers has been improved by pre-injection in epitaxial growth, surface treatment just before bonding, high temperature annealing at bonding, high selective etching and hydrogen annealing. The pre-injection reduces defects. The surface treatment eliminates edge-voids. The high temperature bonding dramatically reduces voids all over the wafer. Hydrogen annealing is very effective for surface flattening and boron out-diffusion. In particular, the edge-void elimination by the surface treatment just before bonding is greatly effective for enlarging the SOI area and reduces the edge exclusion down to only two mm. The gate oxide integrity is well evaluated. This process promises high yield and through-put, because each of the steps can be independently optimized.