The thin film transistors (TFTs) based on nitrogen doped zinc oxide (ZnO) were investigated by laser molecular beam epitaxy. The increase of ZnO films' resistivity by nitrogen doping was found and applied in enhancement mode ZnO-TFTs. The ZnO-TFTs with a conventional bottom-gate structure were fabricated on thermally oxidized p-type silicon substrate. Electrical measurement has revealed that the devices operate as an n-channel enhancement mode and exhibit an on/off ratio of 10(4). The threshold voltage is 5.15 V. The channel mobility on the order of 2.66 cm(2) V-1 s(-1) has been determined. (c) 2007 Elsevier B.V. All rights reserved.