A new class of high-vacuum organic deposition chamber was developed to study the structure and growth of organic semiconductor thin films. Using the chamber in situ real-time 2-dimensional grazing incidence x-ray diffraction (2D-GIXD) was measured during thin film growth of distyryl-oligothiophenes derivatives (DS2T) on SiO2 surface. An evolution of 2D-GIXD pattern was clearly observed during the growth due to the crystallization of the molecular domains consisting of standing-up orientation. A theoretical simulation on the experimental 2D-GIXD map provided a potential use of this system to determine the unit cell parameters in thin films. Thickness dependence and influence of air exposure on the film structure were also studied.