The breakdown voltage (V-BD) and breakdown mechanism of junctionless (JL) poly-Si thin film transistor (TFT) were compared to the conventional inversion-mode (IM) TFT using fabricated devices and 3D quantum-corrected hydrodynamic transport device simulation. The simulated results are correspondent with experimental ones. The analyses of electric field distributions in on-state show that the channel of JL devices can equally share the voltage like a resistor, because there are no junctions formed between channel and source/drain. The JL TFT shows excellent breakdown characteristics; the off-state V-BD of 53.4V is several times larger than V-BD of 9.5V in IM TFT with same device size. JL devices have large potential for high voltage power metal-oxide-semiconductor devices and circuit applications. (C) 2013 AIP Publishing LLC.