III-V semiconductor device with integrated power transistor and start-up circuit

We disclose a III-nitride semiconductor based heterojunction power device comprising: a first heterojunction transistor formed on a substrate, the first heterojunction transistor comprising: a first III-nitride semiconductor region formed over the substrate, wherein the first III-nitride semiconductor region comprises a first heterojunction comprising at least one two dimensional carrier gas; a first terminal operatively connected to the first III-nitride semiconductor region; a second terminal laterally spaced from the first terminal and operatively connected to the first III-nitride semiconductor region; a first plurality of highly doped semiconductor regions of a first polarity formed over the first III-nitride semiconductor region, the first plurality of highly doped semiconductor regions being formed between the first terminal and the second terminal; a first gate region operatively connected to the first plurality of highly doped semiconductor regions; and a second heterojunction transistor formed on the substrate. The second heterojunction transistor comprises: a second III-nitride semiconductor region formed over the substrate, wherein the second III-nitride semiconductor region comprises a second heterojunction comprising at least one two dimensional carrier gas; a third terminal operatively connected to the second III-nitride semiconductor region; a fourth terminal laterally spaced from the third terminal in the first dimension and operatively connected to the second III-nitride semiconductor region; a second gate region being formed over the second III-nitride semiconductor region, and between the third terminal and the fourth terminal. One of the first and second heterojunction transistors is an enhancement mode field effect transistor and the other of the first and second heterojunction transistors is a depletion mode field effect transistor.