The imperative for continuous device miniaturization has heightened the need for logic reconfigurability due to its benefits in circuit design simplification and process optimization. Van der Waals ambipolar transistors, notable for their inherent reconfigurable characteristics, have garnered significant interest for their potential to revolutionize information electronics. Nevertheless, as the semiconductor thickness approaches the 3-nm mark, precise modulation of electrical polarity presents a considerable challenge as minor variations in thickness can lead to significant electrical disparities. Here, we introduce a silicon backend process-compatible approach by employing surface charge transfer doping to skillfully adjust the polarity in ambipolar transistors. This universal method can achieve a controllable p-type doping effect and good electrical symmetry in ambipolar semiconductors. Through careful calibration of the MoO3 dopant layer thickness, we significantly enhance the hole mobility in doped WSe2 field-effect transistors (FETs), increasing it from 8 to 100 cm2 V−1 s−1, surpassing the performance of most non-silicon p-type semiconductors. A thorough temperature-dependent doping characterization elucidates the deeper traps-induced Schottky barrier variation for hole transport, and a reduction in current fluctuation for electron transport in WSe2/MoO3 FETs. Leveraging the precision in electrical polarity control, we demonstrate a complementary logic inverter by integrating two doped ambipolar FETs on a single monolithic channel. This advancement paves the way for quasi-forksheet structures and underscores the benefits in evolving advanced processing technologies, steering toward scalable, cost-effective, and efficient electronic device fabrication.