a dual dielectric tri - gate field effect transistor , a method of fabricating a dual dielectric tri - gate field effect transistor , and a method of operating a dual dielectric tri - gate effect transistor are disclosed . in one embodiment , the dual dielectric tri - gate transistor comprises a substrate , an insulating layer on the substrate , and at least one semiconductor fin . a first dielectric having a first dielectric constant extends over sidewalls of the fin , and a metal layer extends over the first dielectric , and a second dielectric having a second dielectric constant is on a top surface of the fin . a gate electrode extends over the fin and the first and second dielectrics . the gate electrode and the first dielectric layer form first and second gates having a threshold voltage vt1 , and the gate electrode and the second dielectric layer form a third gate having a threshold voltage vt2 different than vt1 .