An electronic device can include a channel layer including AlzGa(1-z)N, where 0≤z≤0.1; a gate dielectric layer; and a gate electrode of a high electron mobility transistor (HEMT). The gate dielectric layer can be disposed between the channel layer and the gate electrode. The gate electrode includes a gate electrode film that contacts the gate dielectric layer, wherein the gate electrode film can include a material, wherein the material has a sum of an electron affinity and a bandgap energy of at least 6 eV. In some embodiments, the material can include a p-type semiconductor material. The particular material for the gate electrode film can be selected to achieve a desired threshold voltage for an enhancement-mode HEMT. In another embodiment, a portion of the barrier layer can be left intact under the gate structure. Such a configuration can improve carrier mobility and reduce Rdson.