Poly(3-hexylthiophene) (P3HT) is one of most studied semiconducting polymers due to its high hole mobility, light weight and ease in processing. P3HT has been investigated as the active layer in flexible electronic devices such as transistors, photovoltaics, sensors and light emitting diodes. Flexible P3HT films can be coated on substrates at low temperature from both organic solution and aqueous colloidal suspension, the latter providing a low cost and environmentally friendly processing alternative. Our previous research found that when a droplet of aqueous P3HT colloidal suspensions dried on solid substrate, a coffee-ring would form at contact line due to capillary flow. This coffee-ring effect is undesirable because it inhibits formation of a uniform coating required for good electronic performance. Many proposed methods to eliminate the coffee-ring effect require high-precision, multi-step control or the use of toxic organic solvents. In this work, application of an electric field while coating an aqueous colloidal suspension on electrode-patterned substrate is investigated for more precise assembly. Dielectrophoresis (DEP) was used to prevent the coffee-ring formation and to assemble particles into more ordered structures. Under the DEP field, particles will assemble into chains and monolayers, then settle to the surface of the substrate, which provides higher resistance to capillary flow and preventing the particles from flowing outward to the droplet edge thus creating more uniform coating. The resulting coatings are manufactured into field effect thin film transistors and electronic performance is characterized. The effects of drying conditions, DEP parameters and suspension concentrations on uniform coating and corresponding device performance are studied. Conclusions are drawn regarding the relative strength of capillary, DEP and gravitational forces during drying.