By introducing the UV beam into our homemade chemical vapor deposition system, We had obtained a welt aligned SWNT array on an ST-cut quartz substrate. After transfer onto a SiO2/Sl substrate, the SWNT array was detected by Raman spectroscopy and electrical measurement, which showed that over 95% of the SWNTs were semiconducting ones. It is proposed that the selection process took place at the very beginning of the SWNT formation rather than destroying the metallic SWNTs after growth. This approach has solved one of the most important problems in SWNT application.