The reliability of vanadyl-phthalocyanine (VOPc) thin filmtransistors (TFTs) with silicon nitride (SiNx) gate insulator was investigated under bias stress conditions. The shift of threshold voltage in ambient air, in vacuum and at high temperature was discussed. The initial field-effect mobility and threshold voltage were 1.2 cm(2)/Vs and -4.22 V, respectively. After a gate bias stress of -20 V for 10,000 s in ambient air, the threshold voltage showed a small shift of less than 0.6 V. In vacuum at high temperature, the shifts of threshold voltage were also below 1 V and current change of devices under the same bias condition was negligible. The excellent reliability was attributed to the reduction of interface defect states between VOPc film and SiNx gate insulator. These results show that VOPc TFTs using SiNx insulator hold a great promise of application in active-matrix organic light emitting displays. (C) 2013 Elsevier B.V. All rights reserved.