Star-shaped polyhedral oligomeric silsesquioxane (POSS)–methacrylate hybrid copolymers with phenyl–triazole as terminal groups had been designed and synthesized via sequential atom transfer radical polymerization (ATRP), azidation, and phenylacetylene-terminated procedures, and the hybrid copolymers here could be denoted as POSS–(PXMA-Pytl)8, where X can be M, B, L, and S, represented four different methacrylate monomers, such as methacrylate (MMA), butyl methacrylate (BMA), lauryl methacrylate (LMA), and stearyl methacrylate (SMA), respectively. Thermal gravimetric analysis (TGA) and in situ Fourier transform infrared spectroscopy (FTIR) were applied for studying the thermal stability and degradation mechanism, and it was found that all of the POSS–(PXMA-Cl)8 and POSS–(PXMA-Pytl)8 copolymers exhibited excellent thermal stabilities, which had great potential in heat-resistant material application. Different tendencies of decomposition temperatures at 5% and 10% weight loss (T5 and T10) dependent on the side-chain length and terminal group species were investigated respectively. The longer alkyl side chains of the monomers, the lower thermal stabilities, and enhanced T5 and T10 were also shown with the introduction of phenyl–triazole groups instead of chlorine groups. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40652.