This work explores a new technique for 3D aspherical Si microlens fabrication using a shadow mask. With the shadow mask, a convex aspherical SiO 2 layer is sputter deposited on a Si wafer due to the anisotropy of deposition. The shape of the SiO 2 is transferred to Si by DRIE to form the aspherical microlens. Microlenses with controllable apertures (0.4μmm - 2mm in diameter) and focal lengths (1mm - 12mm) can be fabricated using this simple, mass-production compatible and cost-effective method. The optical simulation verified the focal effect of the lens, which can be applied to infrared optics. Furthermore, a self-focusing acoustic transducer is fabricated using the Si microlens as a mold, providing potential good self-focusing effect for actuations and sensing.