The present application discloses provides a method for planarizing an interlayer dielectric layer, comprising the steps of: providing a multilayer structure including at least one sacrificial layer and at least one insulating layer under the sacrificial layer on the semiconductor substrate and the first gate stack, performing a first RIE on the multilayer structure, in which a reaction chamber pressure is controlled in such a manner that an etching rate of the portion of the at least one sacrificial layer at a center of a wafer is higher than that at an edge of the wafer, so as to obtain a concave etching profile; performing a second RIE on the multilayer structure to completely remove the sacrificial layer and a part of the insulating layer, so as to obtain the insulating layer having a planar surface which serves as an interlayer dielectric layer. The planarization process can replace a CMP process for providing an interlayer dielectric layer having a planar surface, which achieves a relative larger available area of the wafer.