Abstract: The present invention relates to formation of trench isolation structures that isolate active areas and a preferred doping in the fabrication of a CMOS device with a minimized number of masks. P-type dopant are implanted into a semiconductor substrate having therein a P-well and an N-well. Each of the N-well and P-well has therein a trench. The P-type dopant are implanted beneath each of the trenches in the P-well and the N-well to create a first P-type dopant concentration profile in the semiconductor substrate, wherein the P and N wells are substantially unimplanted by the P-type dopant in active areas adjacent to the respective trenches therein. A second implanting P-type dopant is made into the semiconductor substrate. The second implanting is beneath each of the trenches in the P and N wells to form a second P-type dopant concentration profile.