Ceramics are hard, light-weight, and thermally stable, but are not used in structural applications due to their brittleness. If toughened, ceramics can be an effective alternative to metals that are heavy but used in the high-temperature or armor applications. Ceramic toughening is currently achieved by introducing fiber reinforcements to arrest and/or deflect crack initiation and propagation, or by compositing with ductile phases (metals and polymers). To further improve fracture toughness without compromising thermal stability, we propose a new hierarchical, all-ceramic micro-structure consisting of small-sized grains with “soft” interphase layers, including nano-porosity. Traditionally, pores are considered as defects, but when pores are very small (<~100 nm), the nano-pores deform locally in a non-propagating manner; such local quasi-plastic deformations are expected to improve fracture toughness. Meanwhile, grain sizes are decreased to compensate for the decreased stiffness due to such “soft” interphase layers. In this work, boron carbide is selected as a model system because of their high hardness, low fracture toughness, and effectiveness in shield radiation. Field-assisted sintering technology is selected as a scalable manufacturing method with tunable micro-structures. The fabricated samples are tested for stiffness, hardness, and fracture toughness at room temperature, and studied in relation with their micro-structures.