A double-sided micromachining process for silicon-based device fabrication is developed that allows the use of capacitively coupled reactive ion etching (RIE) equipment for high-aspect-ratio etching. The effects of the masking materials and RIE conditions are discussed. Based on the experimental results, a 1000-Å-thick Al film sufficiently protects the unexposed substrate while allowing the etching of a 350-μm-deep hole with an area of 3×3 mm2 when etching with plasma. A 2000-μm-long and 100-μm-wide (with layers of and thickness of 0.1/2.2/40 μm, respectively) cantilever beam is achieved. A silicon etch rate up to 2.5 to 2.8 μm/min is obtained and an anisotropy of where is the horizontal undercut and H is the etch depth) is obtained. The technique is developed mainly for bulk micromachining of silicon or composite silicon cantilever structures. © 2005 Society of Photo-Optical Instrumentation Engineers.