The production of high modulus and high strength poly(ethylene terephthalate) fibers was examined by using commercially available melt-spun fibers with normal molecular weight (intrinsic viscosity = 0.6 dL/g). First, molecular weight of as-spun fibers was increased up to 2.20 dL/g by a solid-state polymerization, keeping the original shape of as-spun fibers. Second, the polymerized as-spun fibers were drawn by a conventional tensile drawing. The achieved tensile modulus and strength of as-drawn fibers (without heat setting) were 20.0 and 1.1 GPa, respectively. A heat setting was carried out for the as-drawn fibers. Tensile properties of the treated fibers were greatly affected by the condition of the heat setting. This was related to the increase of sample crystallinity and molecular degradation during the treatments. (c) 2006 Wiley Periodicals, Inc.