Abstract: Compared with alternating current (AC) power distribution systems, direct current (DC) power distribution systems have many advantages, and broad prospects in the deep-sea power supply. This paper presented a DC power electronic transformer (PET) based on quasi series-connected silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET), which can realize high gain isolated power conversion from medium DC voltage (thousands of volts) to low DC voltage (hundreds of volts) under the condition of limited volume. The DC PET can realize high voltage gain with input-series output-parallel connection of multiple isolated buck submodules. In order to match the high voltage on the input side and reduce the volume, a quasi-series-connected SiC MOSFET half-bridge was adopted to improve the input voltage level of submodules and reduce the number of sub modules. In addition, this paper also utilized the bare dies to build the DC PET. Dielectric liquid was adopted to strengthen the insulation and heat dissipation of the DC PET, which further reduced the volume to meet the requirements of in deep-sea applications. A 4.5kV/680V/30kW prototype was built and verified by experiments.