The influence of horizontal distribution of conjugated poly(3-hexylthiophene) (P3HT) and insulating Poly(methyl methacrylate) (PMMA) on the dispersion and crystallization of organic semiconductor bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) has been studied in this research. Within the vitrified PMMA-rich island like domains, the crystallization of TIPS pentacene was still able to occur and results in scattered crystallites via short-range molecular diffusion. Contrarily, larger clusters of crystallites are able to develop within the molten P3HT-rich domains. During the annealing above the glass transition temperature of PMMA component, the TIPS pentacene prefers to assemble into P3HT-rich domains. However, as the crystallization rate is comparable with the diffusion efficiency, linear crystal growth of TIPS pentacene is observed to propagate across the PMMA domains. Furthermore, the stacking of crystallites of TIPS pentacene within P3HT-rich domains is preferentially along the domain boundaries, reflecting the dominance of nucleation along the boundaries instead of molecular assembly. When the crystallization is less efficient during the annealing above 115 degrees C, TIPS pentacene molecules are able to assemble together within P3HT-rich domains prior to crystallization, causing the absence of TIPS pentacene crystallites within PMMA domains. Accordingly the competition between crystallization and molecular assembly, and also the disparity of chemical affinity of surrounding polymer phases, have been illustrated as the background for the dispersion of crystallites of TIPS pentacene. The distribution of polymer phases is thus realized helpful for the evolution of desired two-dimensional stacking of functional crystals.