The increasing interest in fluorinated 5,11-bis(triethylsilylethynyl)anthradithiophene is motivated by the demonstrated high-performance organic field-effect transistors and circuits based on this organic semiconductor, complemented by reduced complexity processing methods that enable this performance. We identify two polymorphs of this material and report on their crystal structure, formation, and the effect of the different molecular packings on the electronic properties. The polymorphs are interconvertible through a phase transition that occurs at $T=294\text{K}$. We study the variations in the electrical properties as a response to the structural changes induced by the phase transition in both single crystals and thin films, and discuss the technological implications that a room-temperature phase transition has on the performance and stability of devices fabricated with this organic semiconductor.