tA novel method for stepwise in vitro affinity maturation of antigen-specific shark vNAR domains isdescribed that exclusively relies on semi-synthetic repertoires derived from non-immunized sharks.Target-specific molecules were selected from a CDR3-randomized bamboo shark (Chiloscyllium plagio-sum) vNAR library using yeast surface display as platform technology. Various antigen-binding vNARdomains were easily isolated by screening against several therapeutically relevant antigens, includingthe epithelial cell adhesion molecule (EpCAM), the Ephrin type-A receptor 2 (EphA2), and the human ser-ine protease HTRA1. Affinity maturation was demonstrated for EpCAM and HTRA1 by diversifying CDR1 oftarget-enriched populations which allowed for the rapid selection of nanomolar binders. EpCAM-specificvNAR molecules were produced as soluble proteins and more extensively characterized via thermal shiftassays and biolayer interferometry. Essentially, we demonstrate that high-affinity binders can be gen-erated in vitro without largely compromising the desirable high thermostability of the vNAR scaffold.