Gallium Nitride (GaN) devices have increasingly gained traction in power electronic applications due to their superior electrical properties, such as high electron mobility and wide bandgap. This paper presents a unified design approach to integrate GaN devices into high-frequency resonant converters, specifically targeting wireless power transfer (WPT) applications. With the prominence of WPT in sectors ranging from consumer electronics to electric vehicles, there's an impending need for efficient and robust power conversion solutions. By leveraging the high-frequency operation capabilities of GaN devices, this study delves into enhancing the overall efficiency and minimizing converter size. The paper evaluates various GaN device models under different operating conditions and provides design guidelines to achieve optimal converter performance. A comparative analysis is also made with traditional Silicon (Si) based devices to underscore the advantages offered by GaN technology. Experimental results from prototypes underscore the efficacy of the proposed design approach, revealing substantial improvements in efficiency and power density. This work paves the way for a new generation of resonant converters, capable of meeting the stringent demands of modern WPT systems.