Organic field-effect transistors utilizing solution-processed benzothieno-benzothiophene is developed using a three-dimensional field-effect transistor structure, which comprises multiple vertical channels to enhance their output drain current. The soluble benzothieno-benzothiophene thin films were formed on vertical channels using different solvents, and the mobility is estimated to be 3.7x10-3cm2/Vs. Nevertheless, extremely large values of channel width divided by length enables current amplification up to 0.7mA per device area of 1cm2, even with the low carrier mobility. The result demonstrates the usefulness of the three-dimensional structure to produce high output currents for device applications.