GaN high electron mobility transistors (HEMT) are becoming the mainstream for high frequency and power switching applications. Devices and circuits based on these emerging materials are more suited to operate at higher voltages and temperatures than Si-based devices owing to their superior physical properties. Recently, AlGaN/GaN based high electron mobility transistors (HEMTs) on low cost silicon substrate have been extensively demonstrated as attractive candidates for next generation power devices in the 100-650V range with low on-resistances. On the other hand, Ultra-Wide Band Gap (UWBG) materials such as AlN that has a bandgap of 6.2 eV are attracting attention for pushing the limits and address new requirements of high voltage power devices. In this presentation, we will discuss various device designs and preliminary results already showing the advantages and benefits of these new material systems for high voltage applications.