Electric bicycles (e-bikes), as a zero-emission vehicle, have been considered as an effective solution by authorities and researchers to reduce pollution. Research activities in this field are to increase the efficiency of electric motor drives, and power management units of electric bicycles, and in particular to increase the efficiency and power density of power converters used for power supply and distribution. In light of recent advances and deployment of wide-band-gap (WBG) semiconductors, capable of operating at high-voltage and high-frequency compared with their silicon counterparts, power converters can be designed and implemented with higher efficiencies, smaller size, and higher power densities. Recently, the use of WBG semiconductors has been widely considered to improve battery charger performance in automotive and electric vehicle applications. For example, the use of WBG semiconductors in a battery charger circuit of an e-bike can significantly reduce the size and power loss of the battery charger. In this thesis, the characteristics and performance of WBG transistors compared to silicon ones specifically for step-down (buck) converters in battery charger applications for e-bikes. In this regard, while introducing the structure of these new transistors, their performances specifically in e-bike applications are investigated in terms of the conductive and switching losses, switching frequency, power density, weight and efficiency of the buck converter for an e-bike battery charger. However, at high switching frequencies, the switching losses of WBG transistors are significantly higher than the total switching losses. As the conventional method of calculating the Si-transistor switch losses is not sufficiently accurate for WBG transistors, a model for estimating the switching losses of WBG transistor at high switching frequencies is required. Such a model should take the parasitic inductors and capacitors of WBG-transistor into account. The thesis suggests such a model and presents a method for calculating the model parameters. The validity of the proposed model is verified through the simulation compared with the test results obtained based on experiments.