Chemical Mechanical Planarization (CMP) is an important process in semiconductor chip fabrication. In the CMP process, excess material is removed and the surface is planarized by the action of chemical and mechanical forces. Shallow Trench Isolation (STI) has become a key technology for device isolation in recent times. In this method, a shallow trench is made on the silicon wafer between active devices, silicon dioxide is deposited over the trench as well as the active area and the excess silicon dioxide is removed by CMP. The oxide remaining in the shallow trench would isolate the transistors. High selectivity can be achieved by adding certain chemicals that inhibit nitride polish rate without changing the oxide polish rate significantly. The effect of hydrogen peroxide in chemical mechanical planarization slurries for shallow trench isolation was investigated. The various abrasives used in this study were ceria, silica, alumina, zirconia, titania, silicon carbide, and silicon nitride. Hydrogen peroxide suppresses the polishing of silicon dioxide and silicon nitride surfaces by ceria abrasives. The polishing performances of other abrasives were either unaffected or enhanced slightly with the addition of hydrogen peroxide. The ceria abrasives were treated with hydrogen peroxide, and the polishing of the work surfaces with the treated abrasive shows that the inhibiting action of hydrogen peroxide is reversible. It was found that the effect of hydrogen peroxide as an additive is a strong function of the nature of the abrasive particle.