The visco-elastic oxidation model has been calibrated on 0.35 and 0.25 mu m CMOS LOGOS-type isolation structures. Simulation is used to assess the capability of advanced LOGOS options for sub-0.25 micron CMOS. At reduced active area pitch the active-area lifting phenomenon restricts the thickness of field oxide which may be grown. Predictions of the maximum field oxide and active ar ea encroachment are made for an active area pitch of 0.6 mu m.