The development of integrated circuits (ICs) based on a complementary metal-oxide-semiconductor through transistor scaling has reached the technology bottleneck; thus, alternative approaches from new physical mechanisms are highly demanded. Valleytronics in two-dimensional (2D) material systems has recently emerged as a strong candidate, which utilizes the valley degree of freedom to process information for electronic applications. However, for all-electrical valleytronic transistors, very low room-temperature "valley on-off" ratios (around 10) have been reported so far, which seriously limits their practical applications. In this work, we successfully illustrated both n- A nd p-type valleytronic transistor performances in monolayer MoSand WSedevices, with measured "valley on-off" ratios improved up to 3 orders of magnitude greater compared to previous reports. Our work shows a promising way for the electrically controllable manipulation of valley degree of freedom toward practical device applications.