A method of fabricating a complementary metal-oxide-semiconductor device is provided. The method includes forming a work function material layer segment on a gate dielectric layer over a first vertical fin and a bottom spacer layer on an n-type bottom source/drain adjoining the first vertical fin on a first region of a substrate, wherein the gate dielectric layer is also over a second vertical fin, bottom spacer layer on a p-type bottom source/drain adjoining the second vertical fin on a second region. The method further includes heat treating the work function material layer segment to produce a modified work function material layer segment on the first vertical fin with a shifted work function value, forming a second work function material layer on the modified work function material layer segment and the gate dielectric layer on the second vertical fin, and growing a top source/drain on each of the vertical fins.