We report the synthesis of a new high-temperature liquid-crystalline thermoset based on the phenylethynyl functional group. The monomer was a nematic thermotropic liquid crystal with a melting temperature of 268 degrees C. The extrapolated onset of the cure exotherm occurred at 313 degrees C. The cured thermoset retained the nematic liquid-crystalline order of the parent monomer. The monomer and crosslinked resin were characterized by differential scanning calorimetry, optical microscopy, and thermogravimetric analysis. The thermal stability of the crosslinked resin was determined in both air and nitrogen atmospheres at various heating rates. The onset of weight loss in air and nitrogen atmospheres was determined to be 397 and 422 degrees C, respectively, for a heating rate of 10 degrees C/min.