The use of a thick channel layer (Tch) with a locally etched region and a NiO capping layer (CL) thereon to release the trade-off between the dark current (Idark) and photo current (Iph) of UV photodetector based on SZTO TFT is demon-strated. The influences of the Tch and final thickness (Tchf) af-ter local etching, and NiO CL on the optoelectrical properties of SZTO TFTs are investigated. Experimental results show that the 100-nm-thick SZTO TFT with a Tchf of 40 nm and a NiO CL has excellent in Rph and Sph up to 1972 A/W and 1.9×10^7 A/A under UV irradiation at 275 nm, which are about 303 and 251 times larger than the conventional 30-nm-thick SZTO TFT. It’s attributed to the use of a thick Tch and the formation of NiO CL/SZTO pn heterojunction maximize the harvest of photogenerated carriers to cause more negative ΔVth of TFT to boost Iph under UV irradiation, in addition, a thin effective Tch obtained from the local etching together with NiO CL is very effective in lowing Idark.