According to one embodiment, a high electron mobility transistor (HEMT) comprises an insulator layer comprising a first group III-V intrinsic layer doped with a rare earth additive. The HEMT also comprises a second group III-V intrinsic layer formed over the insulator layer, and a group III-V semiconductor layer formed over the second group III-V intrinsic layer. In one embodiment, a method for fabricating a HEMT comprises forming a first group III-V intrinsic layer and doping the first group III-V intrinsic layer with a rare earth additive to produce an insulator layer. The method also comprises forming a second group III-V intrinsic layer over the insulator layer, and further forming a group III-V semiconductor layer over the second group III-V intrinsic layer. A two-dimensional electron gas (2DEG) is formed at a heterojunction interface of the group III-V semiconductor layer and the second group III-V intrinsic layer.