ABSTRACTWe have investigated the structure of a-Si:H thin films using variable coherence transmission electron microscopy. Variable coherence is a new microscopy technique that is sensitive to higher-order atomic position correlations. We observe changes in the structure of α-Si:H with increasing hydrogen content and with light soaking. Based on these observations we conclude that a less ordered form of α-Si:H is more structurally stable than a more ordered form. This may have implications for understanding the Staebler-Wronski effect.