Directional controllability of single-walled carbon nanotubes (SWNTs) is an important issue for future nanoelectronics applications. For direct integration of carbon nanotubes with modern electronics, aligned growth of carbon nanotubes on SiO(2)/Si is desirable. We developed a new method to horizontally align SWNTs directly on SiO(2)/Si substrate by creating trenches on Si(100) through anisotropic etching followed by thermal oxidation. The V-shaped trenches highly improved the alignment of SWNTs and the degree of alignment is comparable to the step-templated alignment of carbon nanotubes on crystals. The trenches also improved the density of aligned nanotubes due to the combination of "trench-guided" and gas-flow guided alignment. Our new insights on carbon nanotube alignment on SiO(2)/Si will greatly contribute to future large-scale nanoelectronic applications.