The potential of polymer-derived ceramic matrices for silicon-carbide fiber composites is demonstrated by additive layering of thin films on SiC fiber bundles. The thin liquid films, which naturally wet the fiber surfaces, are cross-linked and pyrolyzed in-situ into the silicon carbonitride ceramic in just a few seconds to yield defect-free layers that are 10 to 100 nm thick. The infiltration is completed by repeating the cycles. A nearly fully dense and defect free SiCN matrix could be obtained. Room-temperature tensile tests show a tensile strength of similar to 1200 MPa. Good matrix-fiber interface behavior is seen with pull-out character which is most likely responsible for the apparent ductility. The SiC fibers were uncoated.