A structure for an III-V integrated circuit includes an integrated depletion and enhancement mode gallium nitride high electron mobility transistors (HEMTs). The structure includes a first, depletion mode HEMT having a first source, a first drain and a first fieldplate gate between the first source and the first drain, and a second, enhancement mode HEMT having a second source and a second drain. The second HEMT also includes a gallium nitride (GaN) gate and a second fieldplate gate between the second source and the second drain. The second fieldplate gate of the second HEMT may be closer to the second drain than the GaN gate. The structure provides a reliable, low leakage, high voltage depletion mode HEMT (e.g., with operating voltages of greater than 100V, but with a pinch-off voltage of less than 6 Volts) integrated with a gallium nitride (GaN) gate-based enhancement mode HEMT.