The effect of the induced electron traps by oxygen plasma treatment on transfer characteristics of organic thin film transistors (OTFTs) was researched in this study. From the observed result, the relationship between electron trapping and electrical stability of OTFTs was discussed. It is shown that oxygen plasma treatment may lead to a shift of the threshold voltage towards positive gate-source voltages and an increase in the mobility, resulting from the incorporation of oxygen and the passivation of the defects in the grain-boundary region. It is found that the electrical stability mainly arises from the increased long-lifetime electron-trap density.