Abstract: A new method for planarization of shallow trench isolation is disclosed by the wet etching and plasma etching, due to the surface sensitivity of SACVD O.sub.3 -TEOS that depends on substrate. The method described herein includes a pad oxide layer, a silicon nitride layer, and a doped polysilicon oxide layer formed on a silicon substrate. A shallow trench is formed by photolithography and dry etching process to etch the doped polysilicon oxide layer, the silicon nitride layer, the pad oxide layer, and the silicon substrate. A SACVD O.sub.3 -TEOS layer is subsequently formed on the on the doped polysilicon oxide layer and filling into the trench, the deposition rate of the ozone-TEOS layer on the doped polysilicon oxide layer is slower than the deposition rate of the ozone-TEOS layer on the silicon wafer, the wet etching rate of the ozone-TEOS layer on the doped polysilicon oxide layer is faster than the etching rate of the ozone-TEOS layer on the silicon wafer.