The high-speed spinning process of poly(ethylene terephthalate) (PET) was modified by introducing a liquid isothermal bath (LIB) which was kept at a temperature of 155 degrees C and placed at a distance of 150 cm or 200 cm below the spinneret. The structure and mechanical properties of the as-spun fibers thus produced in the take-up speed range of 1 to 7 km/min were characterized The results showed that the introduction of the LIB significantly influences the structural development of the as -spun fibers. The fibers produced using the LIB in the spinline showed significantly higher birefringence and crystallinity compared to the fibers produced using a standard high-speed spinning process. A semi-quantitative numerical simulation was performed with the incorporation of the LIB in the spinline to understand the mechanism of fiber structure formation during the modified high -speed spinning process of PET. The results showed that the solidification stress is considerably high when the solidification was assumed to occur at a position close to the exit of the LIB. The enhancement of molecular orientation was attributed to the increased frictional stress induced by the liquid layer whereas the spinline crystallization was found to be influenced strongly by the temperature of the liquid.