The specific molecular arrangement of triisopropylsilylethynyl (TIPS)-functionalized acenes is widely considered to be the origin of the high performance of TIPS-pentacene thin film devices. However, detailed information on the molecular packing is so far only available for bulk single crystals, and the molecular packing of TIPS-functionalized acenes in thin films has not been directly determined to date. A combination of ultrabright synchrotron grazing incidence X-ray diffraction (GIXD) and crystallographic refinement calculations is utilized to obtain precise information about the molecular packing of two high-performance TIPS-functionalized semiconductors, TIPS-tetraceno[2,3-b] thiophene and TIPS-pentacene, in thin films on silicon oxide.