We have investigated the channel protection layer (PL) effect on the performance of an oxide thin film transistor (TFT) with a staggered top gate ZnO TFT and Al-doped zinc tin oxide (AZTO) TFT. Deposition of an ultra-thin PL on oxide semiconductor films enables TFTs to behave well by protecting the channel from a photo-resist (PR) stripper which removes the depleted surface of the active layer and increases the carrier amount in the channel. In addition, adopting a PL prevents channel contamination from the organic PR and results in high mobility and small subthreshold swings. The PL process plays a critical role in the performance of oxide TFTs. When a plasma process is introduced on the surface of an active layer during the PL process, and as the plasma power is increased, the TFT characteristics degrade, resulting in lower mobility and higher threshold voltage. Therefore, it is very important to form an interface using a minimized plasma process.