There are provided a process for fabricating MEMS device that includes a plurality of through-holes capable being arranged at a high density, the through-holes having a tapered end portion. Through-holes having vertical side surfaces and tapered bottoms are provided by a processing method including the steps of: disposing quadrilateral patterning having desired dimensions on a silicon substrate having a flat surface of a crystal plane, etching the substrate to a desired depth by dry etching that can realize a high aspect ratio etching, and anisotropic wet etching the dry etched substrate with a KOH aqueous solution containing isopropyl alcohol mixed thereinto.