Wide band gap devices are inevitably the future of power electronic converters. However, their high switching speeds make the gate driver design a challenging task. In this way, parameterization of the gate driver resistors is critical to determine the slew rate and consequently the produced power loss and electromagnetic noise of the switch. To address these issues, in this paper, a post-prototyping multi-objective optimization method is introduced in order to parameterize the gate driver resistors. The method then is applied on a GaN-based half-bridge converter to reduce both power loss and electromagnetic noise. To evaluate the electromagnetic noise, near-field EMI of the GaN device is considered. Finally, the experimental results are provided to show the effectiveness of the method.