Solution processable semiconducting polymers with excellent film forming capacity and mechanical flexibility are considered among the most progressive alternatives to conventional inorganic semiconductors. However, the random packing of polymer chains and the disorder of the polymer matrix typically result in low charge transport mobilities (10-5-10-2cm2V-1s-1). These low mobilities compromise their performance and development. Here, we present a strategy-by utilizing capillary action-to mediate polymer chain self-assembly and unidirectional alignment on nano-grooved substrates. We designed a sandwich tunnel system separated by functionalized glass spacers to induce capillary action for controlling the polymer nanostructure, crystallinity, and charge transport. Using capillary action, we demonstrate saturation mobilities with average values of 21.3 cm2V-1s-1 and 18.5 cm2V-1s-1 on two different semiconducting polymers at a transistor channel length of 80 µm. These values are limited by the source-drain contact resistance, Rc. Using a longer channel length of 140 µm where the contact resistance is less important, we measured µh = 36.3 cm2v-1s-1. Extrapolating to infinite channel length where Rc is unimportant, the intrinsic mobility for PCDTPT (Mn = 140 kDa) at this degree of chain alignment and structural order is µh ≈ 47 cm2v-1s-1. Our results create a promising pathway towards high performance, solution processable, and low-cost organic electronics.