Chemical-mechanical planarization or Chemical-mechanical polishing, commonly abbreviated CMP, is a technique used in semiconductor fabrication for planarizing the top surface of an in-process semiconductor wafer or other substrate.

The process uses an abrasive chemical slurry (commonly a colloid) in conjunction with a polishing pad, typically of a greater diameter than the wafer. The pad and wafer are pressed together and rotated at different rates, with different axes of rotation (i.e., not concentric). This removes material and tends to even out any irregular topography, making the wafer flat or planar. This may be necessary in order to set up the wafer for the formation of additional circuit elements, i.e. to bring the entire surface within the depth of field of a photolithography system.

While it was once looked on as too "dirty" to be included in high-precision fabrication processes (since abrasion tends to create particles), CMP became much more widespread in the integrated circuit industry with the move from aluminium to copper conductors. Thick copper features were produced by electroplating, which gives a less uniform and planar result than is possible with other thin-film deposition methods, and so requires some method of planarization. Once this planarization step became necessary, however, other process steps were further optimized to exploit it.