One of the promising material in the field of small molecule semiconductors is 5,11-bis(thiethyl silylethynyl) anthradithiophene (TES-ADT), mostly because of its high charge-carrier mobility, which is, however, strongly dependent on crystal quality and crystal phase of TES-ADT. Several crystal phases of TES-ADT were already reported, but their crystal structure and phase kinetics is still not fully understood. We used X-ray reflectivity and grazing incidence X-ray diffraction to investigate phase transformation dynamics in spin-coated TES-ADT thin films during post growth heating, cooling and quenching. The measurements were performed on a Rigaku SmartLab home-lab diffractometer equipped with an Anton Paar domed heating stage. We show that previously reported phases may coexist at room temperature (RT). Particularly, the alpha phase of TES-ADT appears to be the most stable phase at RT and it is formed out of the amorphous phase with the progress of the time after an annealing treatment. Additionally, we show that the gamma phase may form during cooling the amorphous melt and we demonstrate previously not reported gamma to beta phase transition.