Conjugated, semiconducting polymers have unique prospects for flexible electronic devices such as transistors, photovoltaics and sensors, because they are lightweight, abundant and are inexpensive to process. Poly(3-hexylthiophene) (P3HT) is one of most studied semiconducting polymers due to its solubility, relatively high hole mobility and the ability to synthetically control the chain structure. Flexible P3HT films can be coated on substrates from both organic solution and aqueous colloidal suspension, the latter providing an environmentally friendly processing alternative. This work investigates the production of aqueous suspensions of P3HT using mini-emulsion, and exploits an external AC field for controlling assembly of the particles. The emulsion procedure was found to influence both chain aggregation and colloid size, which in turn affected field effect transistor performance. DEP-assisted assembly helped to prevent particle loss from the transistor channel by counteracting capillary flow. Furthermore, a model polystyrene colloid system was studied to quantify effects of process parameters (relative humidity, particle size and concentration, frequency, field gradient and surface energy) on particle ordering. Ideal parameters were applied to the P3HT system to create improved transistors.