The effect of absorbed moisture on the electrical characteristics and reliability of low dielectric constant materials (low-k) was investigated in this study. The experimental results reveal that porous low-k dielectrics absorb more moisture than dense low-k dielectrics. This absorbed moisture degrades the electrical performance and reliability of both classes of low-k dielectrics. Annealing at a higher temperature of 400 C is required to decompose the physically-adsorbed moisture and thereby restore reliability performance. However, the chemically-adsorbed moisture seems to be difficult to remove by annealing at 400 C, causing a degraded TDDB performance.