Arrays of aligned semiconducting single-walled carbon nanotubes (s-SWCNTs) with exceptional electronic-type purity were deposited at high deposition velocity of 5 mm min(-1) by a novel "dose-controlled, floating evaporative self-assembly" process with excellent control over the placement of stripes and quantity of s-SWCNTs deposited. This approach uses the diffusion of organic solvent on the water-air interface to deposit aligned s-SWCNT (99.9%) tubes on a partially submerged hydrophobic substrate, which is withdrawn vertically from the surface of water. By decoupling the s-SWCNT stripe formation from the evaporation of the bulk solution and by iteratively applying the s-SWCNTs in controlled "doses", we show through polarized Raman studies that the s-SWCNTs are aligned within +/-14 degrees, are packed at a density of similar to 50 s-SWCNTs mu m(-1), and constitute primarily a well-ordered monodispersed layer. The resulting field-effect transistor devices show high performance with a mobility of 38 cm(2) and on/off ratio of 2.2 x 10(6) at 9 mu m channel length.