To improve the thermo-oxidative stability of acetylenic aromatic compounds, 1,2-bis(4-trimethylsilylethynylphenyl)-carborane (CBTMS) was designed, synthesized and characterized by FT-IR, ¹H-NMR, ¹³C-NMR and mass spectrometry. The analysis of the DSC results showed that the acetylenic monomer had a melting point at 195.5 °C. The cross-linking process of CBTMS included a Diels–Alder cycloaddition reaction confirmed by FT-IR spectroscopy. Nonisothermal DSC studies showed CBTMS has an activation energy similar to that of the phenylethynyl-terminated compound. The thermoset and ceramic derived from the acetylenic monomer exhibited extremely thermo-oxidatively stable properties studied using thermogravimetric analysis (TGA). The thermoset showed a weight gain in air at elevated temperature and char yield of 98.8% at 1000 °C in air, and the ceramic residue had almost no weight loss up to 1000 °C in air. We demonstrated that trimethylsilylethynyl could be used as a crosslinking group for thermosetting polymers.