The reaction of trichlorosilane with hexamethyldisilazane results in the formation of a highly branched solid polysilazane of the general formula (HSi(NH)3/2 )x (HSi(N)3/2 )y ((NH)1/2 SiMe3 )z . When the values of x, y and z are 1.0, 0.3-0.6 and 0.4-0.7 respectively, the physical properties of the polymers are appropriate for melt spinning of 10-15 µm diameter fibers. Fibers are crosslinked (cured) on exposure to trichlorosilane. Pyrolysis of the cured fibers leads to amorphous ceramic fibers with up to 3.1 GPa tensile strength and 250 GPa elastic modulus.