Semiaromatic polyamides are used for metal replacementin advancedengineering applications to reduce weight and improve efficiency,but their range of application is limited by their inherent lack ofductility and toughness. Here, we combined semiaromatic polyamidepoly-(hexamethylene terephthalamide-co-isophthalamide) (PA6TI) withup to 30 wt % amine-terminated polyethylene (PE-(NH2)(2)) by high-temperature melt compounding, which was suggestedto lead to the formation of PA-PE block copolymers at the interfacebetween the PE-(NH2)(2) and the PA6TI. This resultedin PA6TI/PE-(NH2)(2) blends with smaller, moreuniform particle sizes than in PA6TI blended with nonfunctional PEor the commercial impact modifier, maleic anhydride-functionalizedstyrene-ethylene-butylene-styrene (SEBS) underthe same conditions. The PA6TI/PE-(NH2)(2) blendsand the corresponding glass fiber-reinforced composites consequentlyshowed significantly greater increases in room-temperature tensileductility and fracture energy with respect to unmodified PA6TI, aswell as maintained mechanical stability at high temperatures, andonly modest decreases in stiffness and strength, even at high PE-(NH2)(2) contents. These improvements were attributedto the crystallinity of the PE-(NH2)(2) particlesand to improved morphological stabilization and matrix-particleadhesion, consistent with the presence of PA-PE block copolymer atthe matrix-particle interfaces.