This paper describes a method for fabricating deep Si trenches with only a wet chemical etching process. A typical photolithography process was used to define the etching area. Aqueous HF/AgNO3 and HF/H2O2 solutions were applied to etch silicon nanowire (SiNW) structures in the selected domains. In the former case, a high selectivity between the bare Si surface and photoresist-covered Si surface can be achieved. The SiNWs with a monolithic < 100 > direction can be etched in the selected domain. However, additional < 010 >- and < 001 >-oriented etchings were observed on the trench sidewall and wafer surface in the latter case. In addition, deep and highly anisotropic trenches were achieved by removing the SiNWs. The Si wafer was immersed in a concentrated aqueous HF/H2O2 solution. A porous structure was formed in the vicinity of Ag nanoparticles, suggesting that one should remove SiNWs completely to achieve deep anisotropic trenches. This method exhibits high anisotropy and is capable of etching deep Si trenches with depths of about 50 mu m without an additional etching mask. It effectively minimizes instrument costs and reveals the potential of large-area fabrication. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3462976] All rights reserved.