In this paper, a new high step-up or high step-down bidirectional DC–DC converter based on GaN HEMT is proposed which can achieve soft-switching characteristics and low switch voltage stress. Based on the conventional tapped inductor DC-DC converter, the presented topology adds a series capacitor and a switch, which not only increases the conversion ratio of the converter but also provides a resonant circuit and creates conditions for soft-switching. To reduce the volume of passive devices, the leakage inductance of transformer is used for resonance. Thus, the system efficiency and power density can be improved in high frequency condition. The operation principles and theoretical analysis of proposed converter are presented in detail. Finally, the experimental results of a 750 kHz prototype circuit with planar coupled inductor are provided to confirm the validity of the proposed topology.