Two planarization approaches of the oxide-filled trench isolation have been evaluated. Results show that the oxidefilled shallow-trench isolation technology based on a chemical-mechanical polishing (CMP) process is difficult to control and has a poor uniformity. It also results in a dishing effect in wide field regions. On the other hand, a new planarization process can achieve an excellent uniformity and fully planar surface by using a combination of a masking polysilicon layer based on a CMP process, selective wet etching for oxide refill on active regions, short-time CMP process for oxide refill, and reactive ion etching etchback. Results also show that the high breakdown yield of the gate oxide and the low leakage current of the n+/p junction diodes with the novel planarization process demonstrates extremely low defect density from this process. This new process is a very promising candidate for oxide-filled shallow-trench isolation.