Integrated circuitry comprising a ribbon or wire (RoW) transistor stack within which the transistors have different threshold voltages (Vt). In some examples, a gate electrode of the transistor stack may include only one workfunction metal. A metal oxide may be deposited around one or more channels of the transistor stack as a solid-state source of a metal oxide species that will diffuse toward the channel region(s). As diffused, the metal oxide may remain (e.g., as a silicate, or hafnate) in close proximity to the channel region, thereby altering the dipole properties of the gate insulator material. Different channels of a transistor stack may be exposed to differing amounts or types of the metal oxide species to provide a range of Vt within the stack. After diffusion, the metal oxide may be stripped as sacrificial, or retained.