A method of manufacturing a transistor, includes: (i) forming a metal-oxide semiconductor layer over a substrate; (ii) forming a source electrode and a drain electrode on different sides of the metal-oxide semiconductor layer; (iii) forming a dielectric layer over the source electrode, the drain electrode, and the metal-oxide semiconductor layer; (iv) forming a hydrogen-containing insulating layer over the dielectric layer, in which the hydrogen-containing insulating layer has an aperture exposing a surface of the dielectric layer, and the aperture is overlapped with the metal-oxide semiconductor layer when viewed in a direction perpendicular to the surface; (v) increasing a hydrogen concentration of a portion of the metal-oxide semiconductor layer by treating the hydrogen-containing insulating layer so to form a source region and a drain region; and (vi) forming a gate electrode in the aperture.