We report optimized precise alignment of individual single-walled carbon nanotubes (SWCNTs) by the resist-assisted AC-dielectrophoresis (DEP) method. We can reproducibly control the alignment precision to sub-50 nm by customizing the critical DEP parameters, such as: applied AC signal, trapping time, solution concentration, intrinsic properties of the CNTs and so on. The self-aligned CNT field-effect transistors (FETs) have proven to be electrically robust. Therefore, this method holds promise for bottom-up fabrication of high-quality nanoelectronic devices for digital and analog applications with high yield and uniformity.