Abstract This paper presents a high‐power‐density solid‐state transformer (SST) designed for 25 kV alternative current railway applications, delivering a 3 kV direct current output to traction inverters. The SST is composed of sub‐modules with the adoption of 1.7 kV insulated gate bipolar transistor and SiC metal oxide field effect transistor (MOSFET) in an input‐series–output‐series structure, providing higher power density than conventional topologies that rely on high‐voltage switches (>1.7 kV). Because these high‐voltage SiC MOSFETs are still expensive and not fully commercialised, the proposed approach offers a more cost‐effective alternative. A total of 42 converter cells ensure a highly modular and scalable design, with precise synchronisation and high‐speed control achieved through an EtherCAT‐based communication network. Additionally, a distributed control algorithm is introduced, mitigating excessive dependence on the communication link for module‐level operations. The effectiveness of the entire system—including the design and control schemes—has been experimentally verified, ranging from individual converter cells to a reduced SST prototype of up to three sub‐modules. These results confirm the feasibility and advantages of the proposed SST in terms of power density, cost efficiency and reliability for railway traction applications.