Two-dimensional transition metal dichalcogenides (2D TMDs) with metal-insulator transition (MIT) have garnered significant attention for their potential in elucidating electronic state regulation mechanisms and advancing novel electronic devices, ultra-low power switches, and memory technologies. Generally, MIT behavior is often obscured by Schottky barrier (SB). Previous approaches, such as using four-probe methods or barrier-free van der Waals (vdW) semimetal electrodes, have aimed to eliminate the influence of SB on MIT. However, these methods are either complicated by intricate fabrication and testing processes or limited by the availability of suitable semimetal electrodes. Here, we demonstrated a bias voltage (V_ds)-switchable MIT in pure vdW TMDs field-effect transistors (FETs) for the first time, driven by V_ds-tunable effective SB and charge injection mechanisms. We identified a conversion voltage (V_conversion), which can be reduced by eliminating extra tunneling barriers introduced by vdW gaps before the inherent SB. This work offers comprehensive perspective on how tunneling barriers influence MIT and introduces a straightforward approach to fabricating MIT-based electronic devices.