Polymer-matrix composites (PMCs) have become an integral material in many industries due to excellent strength-to-weight ratio and low cost. When semi-crystalline polymer thermoplastics, such as polyethylene terephthalate (PET), are heated past their melt temperature then cooled during compression molding, the long polymer chains in the amorphous regions unravel and align to form crystalline regions with improved strength and stiffness. This research aimed to understand the effect of compression molding processing parameters such as temperature, pressure, dwell, and cooling rate as well as the overall panel thickness on crystallinity and mechanical properties of unidirectional glass fiber-reinforced PET. It was found that a slower cooling rate and a slightly increased dwell time had the most significant effect on PMC properties. Additionally, uniform crystallinity and scattered mechanical property data taken from specimens throughout thick-section samples suggests there was no symmetric property gradient through the cross-section that affected material performance.