An object of the present invention is to provide a polishing agent for a semiconductor, which is used for polishing a to-be-polished surface of a silicon dioxide-based material layer in the production of a semiconductor integrated circuit device and which is excellent in the dispersion stability and produces less defects such as scratch and has excellent planarization characteristics in polishing. In the present invention, at the production of a semiconductor integrated circuit device, in the case where the to-be-polished surface is a to-be-polished surface of a silicon dioxide-based material layer, the polishing agent for chemical mechanical polishing used when polishing the to-be-polished surface is a polishing agent comprising a cerium oxide particle, a water-soluble polyether amine, at least one substance selected from the group consisting of a polyacrylic acid and a salt thereof, and water, wherein the pH of the polishing agent is from 6 to 9 and the substance above is contained in an amount of more than 0.02 mass % based on the entire mass of the polishing agent.