A process for manufacturing a fiber including polyetherketoneketone including the steps of: mixing polyetherketoneketone and sulfuric acid having a concentration of at least 90 wt % to obtain a spin dope and passing the spin dope through a spinneret into a coagulation bath, wherein the polyetherketoneketone is dissolved in the sulfuric acid to a concentration of 12 to 22 wt %. Also disclosed are fibers obtainable by the process and polyetherketoneketone fibers having a sulfur content of 0.001 to 5 wt %, based on the weight of the fiber, in particular such fibers having low or high crystallinity, as well as, hybrid yarns and composite materials.