Disclosed herein is a polishing slurry and a method of producing the same. The polishing slurry has high selectivity in terms of a polishing speed of an oxide layer to that of a nitride layer used in CMP of an STI process which is essential to produce ultra highly integrated semiconductors having a design rule of 256 mega D-RAM or more, for example, a design rule of 0.13 .mu.m or less. A method and a device for pre-treating polishing particles, a dispersing device and a method of operating the dispersing device, a method of adding a chemical additive and an amount added, and a device for transferring samples are properly employed to produce a high performance nano ceria slurry essential to CMP for a process of producing ultra highly integrated semiconductors of 0.13 .mu.m or less, particularly, the STI process.