Shrinking the device dimension has long been the pursuit of the semiconductor industry to increase the device density and operation speed. In the application of thin film transistors (TFTs), all-organic TFT arrays made by all-solution process are desired for low cost and flexible electronics. One of the greatest challenges is how to achieve ultrashort channel through a cost-effective method. In our study, ultrashort-channel devices are demonstrated by direct inkjet printing conducting polymer as source/drain and gate electrodes without any complicated substrate's pre-patterning process. By modifying the substrate's wettability, the conducting polymer's contact line is pinned during drying process which makes the channel length well-controlled. An organic TFT array of 200 devices with 2 μm channel length is fabricated on flexible substrate through all-solution process. The simple and scalable process to fabricate high resolution organic transistor array offers a low cost approach in the development of flexible and wearable electronics.