We have used scanning tunneling microscopy to study how the Si(5 5 12) surface morphology evolves when exposed to oxygen at elevated temperatures, in particular when both oxide nucleation and etching occur simultaneously. This study includes results for sample temperatures of 650 to 750 degreesC at O-2 pressures of similar to 5 x 10(-7) Torr and exposures of 50 to 600 L. It is already known that the Si(001) surface is significantly disrupted in this transition regime by etch pits and islands caused by etching around oxide-induced pinning sites. For the high-index Si(5 5 12) surface, no etch pits are found on the terraces, but pyramidal or linear islands are observed on terraces and along step edges. Both types of islands incorporate (113) facets, indicating an enhanced stability of this orientation against etching. The absence of etch pits and the presence of well-defined islands qualitatively distinguish the etching behavior of this high-index surface from its low-index counterparts. (C) 2004 American Vacuum Society.