A method of forming shallow trench isolation (STI) regions for semiconductor devices, the method including defining STI trench openings within a semiconductor substrate; filling the STI trench openings with an initial trench fill material; defining a pattern of nano-scale openings over the substrate, at locations corresponding to the STI trench openings; transferring the pattern of nano-scale openings into the trench fill material so as to define a plurality of vertically oriented nano-scale openings in the trench fill material; and plugging upper portions of the nano-scale openings with additional trench fill material, thereby defining porous STI regions in the substrate.