As third-generation semiconductors become commercial, SiC semiconductors are gradually becoming more widely used in LLC resonant converters. The efficiency of the LLC resonant converter is improved by employing soft switching. However, when designing LLC resonant converters, semiconductors are usually regarded as ideal devices, and their turn-on and turn-off times are neglected. Furthermore, the method of designing the dead time relies on engineering experience and lacks precise theoretical foundations. In order to overcome the shortcomings of the current empirical method and to improve the generality and practicality of the dead time design method, a novel method for calculating the dead time of full-bridge LLC converters is proposed through theoretical research based on the operating principle of full-bridge LLC converters and the conditions for implementing soft switching. The method takes into account the switching characteristics of semiconductors and the on-state delay time of their body diodes, stray inductance, drive circuits, and errors arising from the first harmonic approximation (FHA) and improves the accuracy of the dead time calculation. It can implement good soft switching with full-bridge LLC converters, reduce switching losses, and improve system efficiency. Finally, the simulation experiment and the 2 kW experimental prototype are built to verify the effectiveness of the proposed method.