A method of making a channel region in a semiconductor device includes providing a substrate having a first transistor area arranged adjacent to a second transistor area; growing an epitaxial layer on the second transistor area of the substrate; forming a trench in the substrate between the first transistor area and the second transistor area; performing a condensation technique to thermally mix materials of the epitaxial layer and the substrate; and filling the trench with a dielectric material to form a shallow trench isolation region between a first channel region of the first transistor and a second channel region of the second transistor; wherein performing the condensation technique is performed after forming the trench.