We have successfully integrated microfluid flow channels, defined by surface energy differences, with thin-film organic field-effect transistors. The device performance is stable for specific semiconductors with water flowing over the channel region and the contacts protected by hydrophobic surface films, indicating that organic semiconductors are not necessarily degraded by water even when carrying current. In addition, a substantial response from dilute organic solutes, as low as 1 ppm in an aqueous environment, can be observed, with some degree of semiconductor-solute specificity.