Arrays of organic thin-film transistors (TFTs; see Figure) were fabricated using self-aligned microfluidic channels. The self-aligned fluidic channels defined the active area of the TFTs and provided pixel-to-pixel isolation. TFTs made with a regioregular poly(thiophene) had field effect mobilities of 0.05 cm(2) V-1 s(-1) and on/off current ratios of 10(8).