A method for manufacturing a strained channel MOS transistor including the steps of: forming, at the surface of a semiconductor substrate, a MOS transistor comprising source and drain regions and an insulated sacrificial gate which partly extends over insulation areas surrounding the transistor; forming a layer of a dielectric material having its upper surface level with the upper surface of the sacrificial gate; removing the sacrificial gate; etching at least an upper portion of the exposed insulation areas to form trenches therein; filling the trenches with a material capable of applying a strain to the substrate; and forming, in the space left free by the sacrificial gate, an insulated MOS transistor gate.