With the aim to fabricate nano-silicon-tips with a high aspect ratio,the effect of changing the mask direction on tip shapes was studied.The fabrication processes for nano-silicon-tips using a (100) single crystal silicon wafer by the anisotropic wet etching in the KOH etchant were designed.Based on the experiment and the model of {411} crystal planes,the crystal planes of silicon tips were analyzed.Through discussing the effect of the mask direction on tip shapes,the process parameters to get high aspect ratio nano-silicon-tips were achieved.Experimental results indicate that silicon tips of octahedron and tetrahedron are fabricated with changing mask directions.The direction of mask does not affect the rapid etched crystal planes at the fixed solution concentration and temperature.Nano-silicon-tips are formed by the anisotropic etching in 40% KOH etchant at 78 ℃ and the dry oxidation sharpening in 3 h at 980 ℃,as the square masks are aligning to the 〈110〉 direction.Experiments show that the high aspect ratio of the tip is greater than 2,and the profiles of silicon tips are constituted by {411} crystal planes that intersect (100) crystal planes at 76.37°.