Due to their high quality, the mechanically exfoliated 2D semiconductor nano-flakes are widely employed to study the intrinsic property in basic physics, such as many-body effect, tunable band gap and light-matter interaction. However, the nano-flakes are randomly distributed on the substrate, which makes the device fabrication more complicated. Previous conventional UV exposure and e-beam exposure would let the contact region expose to photoresist or electron beam irradiation, which significantly affects the contact property. Herein, a facile damage-free double exposure is reported, which combines the UV exposure, plasma exposure and optical alignment. The advantage of this strategy is that the contact region would never expose to organic molecular and electron beam irradiation, resulting in an ultra-clean and intrinsic metal-semiconductor interface. The transistor performance as well as the contact property of MoS₂ and WSe₂ semiconductors with the contact of Ti and Pt metals have been systematically studied. The results showed that the room-temperature mobility of WSe₂ reached 155 cm²/Vs (holes) and 160 cm²/Vs (electrons), respectively. By studying the electrical property at low temperature, it was found that the contact barrier could be tuned as large as 358 meV, suggesting its high-efficient band bending and carrier injection. This method provides an important promising fabrication for high performance 2D semiconductor devices.