The extension of fused deposition modeling (FDM) to work with semicrystalline polymers is challenging due to crystallization that occurs during cooling. Conventional characterization methods such as differential scanning calorimetry (DSC) have been used to characterize this behavior; however, the heating and cooling rates available with DSC are much slower than rates experienced during FDM. The recently developed fast scanning calorimetry (FSC) can reach rates of 1000s of degrees C/s. Therefore, the objectives of this research are to evaluate FSC for replicating FDM conditions and to more fully understand the as-processed structure of semicrystalline polymers according to a three-phase model including a mobile amorphous fraction (MAF), a rigid amorphous fraction (RAF), and a crystalline fraction. A case study performed with polyphenylene sulfide showed that cooling rates experienced during FDM could hinder crystallization, while repeated reheating of material at relatively low crystallization temperatures during fabrication could increase the part crystallinity and RAF.