This paper proposes a design procedure in the efficiency of a resonant type half-bridge converter for a high efficiency isolated DC/DC converter. The design procedure is based on the loss calculation. The relationship between the loss element and the efficiency characteristics was clarified. The loss analysis method based on the parameters of the circuit element is formulated. The analysis results agree well with experimental results. In addition, the highest efficiency of 96.8% is obtained using the half-bridge converter. Finally, design procedure in the efficiency was clarified using a design procedure flowchart.