The structure and morphology on different length scales dictate both the electrical and optical properties of organic semiconductor thin films. Using a combination of spectroscopic methods, including scanning near-field optical microscopy, we study the domain structure and packing quality of highly crystalline thin films of oligomeric PQT-12 with 100 nanometer spatial resolution. The pronounced optical anisotropy of these layers measured by polarized light microscopy facilitates the identification of regions with uniform molecular orientation. We find that a hierarchical order on three different length scales exists in these layers, made up of distinct well-ordered dichroic areas at the ten-micrometer-scale, which are sub-divided into domains with different molecular in-plane orientation. These serve as a template for the formation of smaller needle-like crystallites at the layer surface. A high degree of crystalline order is believed to be the cause of the rather high field-effect mobility of these layers of 10(-3) cm 2 V-1 s(-1), whereas it is limited by the presence of domain boundaries at macroscopic distances.