High electron mobility transistors with improved heat dissipation

A semiconductor device having improved heat dissipation, comprising:

• a substrate including a top surface and a bottom surface;
• a nucleation layer on the top surface of the substrate;
• a transition layer on top of the nucleation layer;
• a buffer layer on top of the transition layer;
• a channel layer on top of the buffer layer;
• a barrier layer on top of the channel layer;
• a gate disposed on the barrier layer;
• a via passing through the substrate and the nucleation layer, exposing a bottom of the transition layer, and aligned directly under the gate;
• and
• an electrically conductive metal layer on the bottom surface of the substrate, the metal layer completely filling the via and extending from the bottom surface of the substrate to the bottom of the transition layer above the nucleation layer.