In this chapter, we discuss III-nitride lateral transistors for power switching applications. GaN-based transistors have the capabilities of delivering high current, handling high voltage, and switching at high speed. These are exactly what are needed for the next-generation power electronics with better efficiency, smaller form factor and lower cost. Development of GaN power switching transistor largely leveraged the work done for making GaN microwave transistors. In order for the GaN transistors to be used for power switching, several modifications to the GaN microwave transistor technology needs to be made. One is the normally-off operation. Power electronics circuits require the switches to be normally-off for safe circuit startup. A second one is the high-voltage operation. While most of today's microwave transistors operate between 28 and 48 V, power switching transistors often operate at 400–480 V. A third one is the use of Si substrates. While GaN-on-SiC structures are most common for microwave transistors, GaN-on-Si structures are needed for power switching transistors for lower cost and better manufacturability. In Section 1, we discuss technologies to enable normally-off operation. In Section 2, we discuss high-voltage operation of GaN transistors. In Section 3, we discuss impact of using Si substrates on power switching characteristics. In Section 4, we discuss factors limiting the performance of GaN-on-Si lateral transistor power switching performance.