This paper presents a new topology for a fully bidirectional soft-switching solid state transformer (S4T). The minimal topology, featuring 12 main devices and a high-frequency transformer, does not use an intermediate DC voltage link, and provides sinusoidal input and output voltages. The S4T can be configured to interface with two-or multi-terminal DC, single-or multi-phase AC systems. An auxiliary resonant circuit creates zero-voltage-switching (ZVS) conditions for main devices from no-load to full-load, and helps manage interactions with circuit parasitic elements. The modularized structure allows series and/or parallel stacking of converter cells for high-voltage and high-power applications.