Ultra-wide bandgap (UWBG) semiconductors are attracting increasing research interest for power device applications. While promising results have been reported for various materials, it remains unclear which material and technology will succeed. Many figure of merits (FOMs) were derived for power device applications to guide material choices, including the widely used Baliga’s FOM (BFOM) to describe the resistive loss of power devices, and Baliga’s high-frequency FOM (BHFFOM) to further consider the switching loss. However, key underlying assumptions for those widely cited FOMs, including the assumption of shallow hydrogenic dopants, tend to fail for UWBG semiconductors. In this work, we revisit several important FOMs in describing vertical power electronics to properly account for both incomplete ionization and background compensation effects. We suggest that it is necessary to include the dopant ionization term (for example n/Nd in an n-drift layer) for both BFOM and BHFFOM to fully capture the potential of the UWBG semiconductors for power device applications. Incomplete dopant ionization in materials like diamond and AlN substantially lowers their FOMs for power switching, leading to high conductive and switching losses. Due to the availability of shallow donors, low background impurity compensation, and bulk substrates, β-Ga2O3 promises the best performance among the investigated materials. The modified FOMs offer a valuable guidance in material choices for power device applications.