Well aligned Si nanowires (SiNWs) by Vapor-Liquid-Solid growth process are presented. Instead of using H2, the current work uses N2 as carrier gas. The growth conditions of SiNWs are controlled by the ratio of nitrogen versus silane gas. Tapering of nanowires was found at T=620°C and P=333 m torr, and the tapering parameter was reduced by increasing the N 2 gas. Tapering of nanowires is attributed to volume reduction of Au catalyst which diffuses onto the side wall of nanowires. However, it is found that the N2 gas has a similar effect of O2 gas which can reduce diffusion of Au catalyst so that volume reduction of Au catalyst is not so significant and nanowire growth becomes untapered. By adopting reflow of photoresist techniques, the size of metal catalyst for SiNWs growth can be significantly reduced, and the growth location of SiNWs can be defined. Well aligned Si nanowires can be obtained. However, aspect ratio of the nano size hole in the photoresist after reflow has a significant effect on the amount of the Au in the nanoparticles and thus the quality and growth of the nanowires.