Using ZnO, and three compositional In(2)O(3)-Ga(2)O(3)-ZnO (IGZO, In:Ga:Zn=1:1:1, 2:1:2, 2:2:1, atomic ratio) semiconductors, we have made and evaluated several double layered oxide thin-film transistors (TFTs). The drain current was mainly affected by the nearer channel material to a gate insulator. From the positive bias stress (PBS) tests, however, the electrical stability showed a complicated result, depending on both channel structures and post-heat treatments. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.