We studied the gas permeation properties of poly(ether ether ketone) (PEEK) and compared it with two other polymers commonly used in the construction of semiconductor microenvironments, polycarbonate (PC), and poly(ether imide) (PEI). The PEEK specimens consisted of extruded films as well as compression- and injection-molded specimens. The compression-molded specimens were prepared to achieve the highest crystallinity. Injection-molded disks, representing products, were milled to a prescribed thickness. Permeation, diffusion, and solubility coefficients were measured on these various PEEK specimens for hydrogen, nitrogen, and oxygen gases. It was found that PEEK generally has better permeation resistance than PC or PEI; showing up to five times lower permeation rates than PC or PEI, depending on grade, crystallinity, and gas. The superior permeation resistance of injection-molded or extruded PEEK, when compared with similarly processed PC or PEI, comes from its crystallinity. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 1637-1642, 2013