In this paper, an isolated high-frequency converter with optimal switch impedance is proposed, which can achieve soft-switching characteristics and a low switch voltage stress. Meanwhile, the topology makes full use of the parasitic components of the transformer, which can reduce the number of system components and improve the system efficiency. The detailed design method of the proposed converter is analyzed. Simultaneously, an air core printed circuit board (PCB) transformer is employed to eliminate the core loss and reduce the vertical space. On the basis of the mathematical analysis, the transformer parameters can be effectively designed. A 20-MHz prototype based on the proposed topology is built. The experimental results verify the advantages of the proposed converter and the corresponding design method.