The SiC devices have been a strong competitor than the conventional Si devices due to the superior characteristics of high operating voltage, low forward voltage, fast switching speed, and high operating temperature. However, the maturity of SiC technology is still in the progress of catching up with the Si devices, the device cost for SiC MOSFET is still much higher than the Si devices. In addition, the maximum current rating of the available SiC devices are still lower than the Si devices, this also limits the utilization of SiC device in high-power applications. In order to combine the Si IGBT’s advantages of low cost and high overload capability and the SiC MOSFET’s advantages of low switching loss. The Si IGBT and SiC MOSFET are connected in parallel as a new switching unit. In this dissertation, the Si IGBT and SiC MOSFET hybrid switch (Si/SiC HyS) in the application of voltage source converters is investigated. The main works are as follows:Firstly, the configuration, conduction characteristic, and switching characteristic of Si/SiC HyS are introduced. The unique dynamic current sharing process and loss modeling for the Si/SiC HyS are analyzed and proposed. The conduction and switching performance are characterized experimentally. Secondly, the operation optimization including the Si and SiC device current rating selection, gate delay time selection, and active thermal control for the Si/SiC HyS are investigated. By using the proposed Si and SiC current rating optimization method, the most cost-effective Si/SiC HyS pairs are obtained for the Si/SiC HyS converter. The optimization of the gate delay time reduces the total semiconductor loss for the Si/SiC HyS and improves the converter efficiency. In order to overcome the thermal unbalance between the Si IGBT and SiC MOSFET, two active thermal control algorithms, named "conduction time variation active thermal control" and "switching sequence dispatch active thermal control", are proposed to reduce the thermal stress of SiC MOSFE. Experimental results validated the effectiveness of the proposed ATC algorithms. Thirdly, the performance of Si/SiC HyS-based converter is improved by the proposed multi-objective operation control. In the light load condition, the converter operates with the conventional gate driving sequence, while in the heavy load condition, the converter’s maximum output power is improved by using the proposed active thermal control algorithms. The experimental results show that the maximum output power of Si/SiC HyS-based buck converter is improved by 5.9%. In addition to the maximum output power improvement, the proposed active thermal control for the Si/SiC HyS can also enhance the converter’s reliability. The reliability enhancement evaluation was investigated based on the UPS inverter application. A mission profile-based converter reliability enhancement evaluation is conducted to assess the yearly accumulated damage reduction on the device bond wire by using the active thermal control. The analysis results show that the yearly accumulated damage on the SiC MOSFET is reduced by 80% by using the proposed active thermal control. Thereby, the useful lifetime of Si/SiC HyS-based converter is extended. Finally, two types of Si/SiC HyS-based three-level active neutral-point-clamped (3L-ANPC) inverter are proposed for high efficiency and low device cost. The proposed Si/SiC HyS-based 3L-ANPC inverters are compared with the full Si IGBT, full SiC MOSFET, and Si with SiC devices-based hybrid 3L-ANPC solutions on the inverter efficiency, power capacity, and device cost. It is shown that compared with the full Si IGBT 3L-ANPC solution, the inverter efficiency improvement by using Si/SiC HyS is 2.4% and 1.8% at light load condition and heavy load condition, respectively. Compared to the full SiC MOSFET solution and 2-SiC MOSFET hybrid scheme, the device cost of 2-Si/SiC HyS-based 3L-ANPC is reduced by 78% and 50% with 0.28% and 0.21% maximum inverter efficiency sacrifices. The testing results show that the proposed Si/SiC HyS-based 3L-ANPC inverter is a cost-effective way to realize high inverter efficiency. Between the two proposed Si/SiC HyS-based 3L-ANPC inverters, the 2-Si/SiC HyS-based 3L-ANPC inverter has lower device cost which makes it more suitable for cost-sensitive and high efficiency applications. While the 4-Si/SiC HyS-based 3L-ANPC inverter has higher output power capacity, making it a better candidate for high power density, high power capacity, and high efficiency applications. Based this work, a 50kW 2-Si/SiC HyS-based 3L-ANPC battery inverter is proposed as a cost-effective and high efficiency solution for the energy storage industry. The design process and testing results are presented.