A novel method for forming substrate contact regions on a SOI substrate without requiring additional space, and in order to provide lower diffusion capacitance. The method utilizes known semiconductor processing techniques. This method for selectively modifying the BOX region of a SOI substrate involves first providing a silicon substrate. Then, ion implanting the base using SIMOX techniques (e.g. O2 implant) is accomplished. Next, the substrate is photopatterned to protect the modified BOX region. Then, further ion implanting using a “touch-up” O2 implant is accomplished, thereby resulting in a good quality BOX as typically practiced. The final step is annealing the substrate. The area of the substrate, which had a mask present, would not receive the “touch-up” O2 implant (second ion implant), which in turn would result in a leaky BOX.