Gallium Nitride (GaN) power transistors are widely used in power products due to the excellent electrical characteristics: high switching speed, high breakdown voltage and low on-resistance, which offer the benefit of a product with smaller size and higher power. Using the silicon substrates manufacturing process, the cost of GaN power transistors is much lower in mass production for higher power products versus silicon power MOSFET’s. However, as a new technology, there are still technical difficulties in GaN power transistor manufacturing. Effective testing in production to screen out the defects to ensure device quality is important. An example is the dynamic on-resistance effect. This presentation will introduce normally off GaN power transistors and the differences compared to traditional silicon power transistor parameters and tests. This includes dynamic on-resistance test requirements and challenges. Also covered will be the Teradyne ETS-88TM test solution showing dynamic on-resistance test plots under stress. The test results will show how the Teradyne ETS-88TM with standard floating source and a proprietary test circuit can not only complete the fast test of dynamic on-resistance, but can also meet mass production test and characteristic analysis of GaN power transistors.