The objective of this Cooperative Research and Development Agreement between Lockheed Martin Energy Research Corporation and Hyper-Therm High-Temperature Composites, Inc. was the optimization of the microstructure of pseudo-porous Sic fiber coatings for Sic/Sic composites. Extensive interfacial test characterization was conducted through single-fiber push-out tests and analytical electron microscopy to assess the effect of various microstructural features of the fiber coating on the interfacial properties of the composite. The thermal stability of these coatings and their interfaces was also investigated after exposure to air at elevated temperatures.