Silicon migration in four nonreducing gas ambients of helium, neon, argon, and nitrogen at a low pressure (10(-3) Torr) and in an ultrahigh vacuum (10(-9) Torr) is studied by monitoring the effect on microfabricated trench structures after a 5 min anneal at 1000 degrees C in each environment. The measurements of the trench corner curvature are used to extract the relative migration rates for each ambient. The migration rate has no ambient gas dependence for the noble gases at 10-3 Torr and has pressure dependence in the 10(-3)-10(-9) Torr range. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3236781] All rights reserved.