High power density (HPD) solid oxide fuel cells (SOFCs) possess the attributes of reduced ohmic polarization and greater active area per unit volume, relative to current state-of-the-art cylindrical SOFCs. Several variations of the basic “flattened tube” HPD geometry are being analyzed and tested. For example, the HPD10 cell enjoys a 58% gain in power density over current practice. In this variation, ten air channels are separated by nine ribs that connect the flat faces of the cell. Other cell geometries, such as the delta cell, and advanced cell materials are under consideration and have the potential for further improvement in power density. The higher power density makes the application of HPD SOFCs to compact auxiliary power units (APUs) attractive. This paper reviews geometric and performance characteristics for HPD cells and presents a conceptual design for an APU of net output.