Deep trenches were etched in single-crystalline silicon for isolation pur-poses using combined dry-wet processing. Reactive ion etching was performed in chlorine-nitrogen plasmas using chloroform, boron trichloride, or sulfur hexafluoride additives to optimize the trench profile. In all cases, however, imperfections such as barreling or micromasking-induced trench bottom residue remained after dry etching A significantly improved profile was obtained with the aid of an additional wet treatment of the dry etched trenches in tetramethyl ammonium hydroxide.