This paper aims at modeling the thermal oxidation of silicon pillars leading to the formation of very sharp silicon tips. The model is used to determine optimum process parameters with respect to the initial shape of the silicon pillars and the geometry of the desired tip. The modeling concept is to extend a previous approach, which predicts the oxidation mechanism of silicon cylinders versus their initial radius. The silicon pillar geometry is approximated by a superposition of silicon cylindrical structures featuring a local curvature radius. Experimental validation has been performed for several initial silicon pillar shapes, at 1000/spl deg/C and 1100/spl deg/C under dry oxidation conditions, leading to formation of very sharp silicon tips. The numerical predictions are shown to agree well with these experimental data. The motivation of this study aims at designing and fabricating a nanoelectromechanical filter device. Its vibrating part consists of a silicon nanotip, covered with a thin gold layer, the geometrical features of which affect the center frequency of the nanofilter device.