We report on the first measurement results to obtain over 2 kV breakdown voltage (V-BD) of GaN-DHFETs on Si substrates by etching a Si Trench Around Drain contacts (STAD). Similar devices without trenches show V-BD of only 650 V. DHFETs fabricated with STAD technology show excellent thermal performance confirmed by electrical measurements and finite element thermal simulations. We observe lower buffer leakage at high temperature (100 degrees C) after STAD compared to devices with Si substrate, enabling high temperature device operation.