Nitride semiconductors have a great potential for high power applications because of a high breakdown field, a very large density of polarization induced two-dimensional electrons, high electron saturation and overshoot velocities, a relatively high mobility, excellent thermal properties, chemical inertness, and radiation hardness. GaN power transistors grown on silicon substrates are already being commercialized. However, while their performance characteristics are competitive or even surpass the best silicon based power transistors, the full potential of the nitride materials for power applications is still to be achieved and will require dramatic changes in the device design that account for the materials properties of wide band gap materials. Such new features include the use of diamond substrates for a better heat removal, adding a low conducting passivation in the high field region between the gate and drain, changing the gate geometry to the perforated channel with perforations extending beyond the gate, using AlInN for lattice matching design to improve stability and reach a high temperature operation and employing lateral-vertical designs and cascade solutions. This presentation will review of the state-of-the –art power GaN based transistors and project the potential improvements in their performance