As the progress of wide-bandgap (WBG) semiconductor devices and the rise of distributed energy resources (DER), medium-voltage solid-state transformer (SST) becomes more and more popular in recent years. Medium-voltage SST features high-performance and fantastic functionality. The SST proposed in this paper is applied in 11.4 kVAC distribution system. The high-voltage terminals are connected in series, and the low-voltage ones are connected in parallel. Steady-state analysis and components design of the converter as well as the parameter design, insulation consideration and loss optimization of the transformer, are described in this paper. Meanwhile, the simulation software SIMPLIS and COMSOL Multiphysics® are used to ensure the validity. Finally, one of 13 modules with input voltage 1.52 kVDC, output voltage 380 VDC and output power 10 kW is designed and realized to verify the feasibility of the prototype converter applied in SST.