A method of manufacturing metal gates comprises the steps of: forming a plurality of parallel trenches on a substrate; forming sequentially a conductive layer and a protective layer on the surfaces of the substrate and trenches; removing the protective layer and conductive layer on the surface of the substrate and the protective layer on the bottom walls of the trenches through anisotropic etching to retain only the protective layer and conductive layer on the side walls; and finally removing the conductive layer not covered by the protective layer through isotropic etching to retain only the protective layer and conductive layer on the side walls so that two insulating gates are respectively formed on the side walls. Thus no isolation material is needed to be disposed at the bottom of the trenches, and the problem of excessive etching to the trenches that results in undesirable insulation can be averted.