A novel technique for the 3D transformation of characteristic sharp corner edges as a result of anisotropic etching of high aspect ratio vertical sidewall silicon punching tools into well-defined round edges by fully-recessed local oxidation of silicon (Locos) is proposed. In a very innovative application of monocrystalline silicon as the tool material for high precision micropunching of thin metal films, silicon punches with vertical sidewalls and characteristic sharp convex cutting corner edges were anisotropically etched in (110) and (100) silicon. The sharp convex corner cutting edges resulted in an earlier tool wear due to critical tensile stress concentration during micropunching process. In FEM simulation results with round cutting edges, Si punching tools showed improved lifetime due to homogeneous distribution of the tensile stress within the tool during micropunching. The proposed idea of corner rounding is initially simulated in CSUPREM simulation software and subsequently experiments are done. The oxide formation during Locos results in a bird’s beak like structure, penetrating under the Si3N4 layer at the convex corner. This bird’s beak like SiO2 formed during Locos eventually consumes the Si atoms to form SiO2, which results in a transformed round corner geometry. The experimental results are compared with the simulation results and are found to be in good agreement. The overall vertical sidewall geometry is well preserved after transformation and the required corner rounding can be precisely controlled with this approach.