A post-cylindrical molecular pump (CMP) sidewall oxidation (PCSWO) has been developed for the shallow trench isolation (STI) process of 0.25 mu m and beyond complementary metal-oxide-semiconductor technologies. One of the most important factors of STI is a round-off of trench top corners without the loss of active area. The conventional STI process usually requires a wall oxidation after trench etch to round off and also an annealing to densify a gap-filled oxide. But PCSWO simplifies the STI process by applying sidewall oxidation and annealing simultaneously. The trench was filled with HDP oxide without the conventional wall oxidation after trench etch. After CMP, post-CMP wall oxide was thermally grown to round off the trench corner at the high temperature of 1100 degrees C. The high temperature wall oxidation has an annealing effect for HDP oxide, which releases a residual film stress. The anomalous subthreshold conduction of the shallow trench isolated metal-oxide-semiconductor field effect transistors as the so called "kink effect" due to field crowding at the active edge, was successfully eliminated even at the back bias of +/-5 V. Isolation and diode characteristics of PCSWO-STI were comparable to those of the conventional STI. Gate oxide reliabilities of PCSWO-STI were similar to those of the conventional STI.