We subjected Organic TFTs to positive and negative constant gate voltage stresses. Stress not only induces temporary charge trapping, but also permanent transconductance degradation. The permanent degradation is accelerated if the devices are stressed under illumination. Negative stress degrades the TFT much faster than the positive stress, at the same voltage. Furthermore, hard breakdowns are observed on devices stressed under light, with VGS= -65V. The degradation mainly comes from stress-induced interface trap generation, rather than photochemical reactions as observed with UV irradiations. © 2013 IEEE.