The stability of low dielectric-constant (low-k) materials during electric-field stress was studied. The dielectric constants (k-values) were found to increase sharply under bias-temperature stress. This time-dependent dielectric-constant increase (TDDI) was estimated for a practical operating condition by extrapolation. The extrapolated TDDI lifetimes and k-value increases for tested materials (k = 2.3-3.2) ranged from 30 days to 1,000 years and from 0 to 23%, respectively. Considering the estimated TDDI, new criteria for reliable low-k materials are proposed. The criteria were used successfully to identify those low-k materials that show high stability during electric-field stress. (C) 2003 The Electrochemical Society.