A new method for fabricating CMOS devices, as well as the resulting devices, is disclosed. The method involves incorporating dopants into a semiconductor substrate through a region of the substrate surface, and diffusing the implanted dopants into the substrate to form a tub. Prior to the diffusion step, a trench is formed in, and extending beneath, the surface which partially or completely encircles the region. The trench serves to prevent the formation, or reduce the size, of a relatively low dopant concentration region, which would otherwise lead to undesirable leakage currents in the completed CMOS device, and prevents latchup.