The ability to produce as-spun poly(ethylene terephthalate) (PET) filaments that possess previously unsurpassed levels of as-spun orientation and tensile properties was achieved through the implementation of a device described as a liquid isothermal bath (LIB). Although much has been published regarding the general effect of the LIE on various properties and structural features, the results of the present study further contribute to the continued development of this unique technology by investigating the positional dependence of the device, as well as the effect of a subsequent annealing process. Characterization methods employed in the present study included birefringence, percent crystallinity, tensile properties, loss tangent temperature dependence, DSC melting behavior, and wide-angle and small-angle X-ray scattering. Strong inferences drawn from the loss tangent temperature dependence indicate that all of the as-spun and annealed LIE filaments possess a more rigid amorphous phase than that present in either the as-spun or annealed no LIE filament and that the extent of rigidness appears to become more profound as the bath is operated at a position more distant from the spinneret. DSC melting endotherms of the as-spun LIE filaments consist of dual overlapping peaks, one component of which is believed to represent the presence of a novel extended chain type of crystalline structure. Application of a simple two phase model allowed for the quantitative evaluation of an amorphous orientation factor, which was found to range, depending on the bath position, from 1.7 to 3.9 times higher in the as-spun LIE filaments than that present in the as-spun no LIE filament. The annealing process was found to play an important role in facilitating the transformation from an as-spun highly oriented and predominantly amorphous structure to a well-defined. semicrystalline fibrillar structure.