Compared to amorphous thermoplastics, semi-crystalline thermoplastics usually have a smaller processing range for thermoforming, due to their narrow temperature window for the transition from viscoelastic to viscous material behavior. On the other hand, semi-crystalline thermoplastics offer superior properties for applications like ductility or chemical resistance. Within this article, modification of semi-crystalline polyamide 12 by radiation cross-linking with respect to its suitability for vacuum thermoforming as well as the effects of processing parameters and sheet thickness on the resulting strain distributions in thermoformed parts are shown. Experimental thermoforming processing studies in combination with digital image correlation measurements, thermo-mechanical and elongational rheometry were performed to characterize the behavior of cross-linked semi-crystalline thermoplastics in the vacuum thermoforming process. POLYM. ENG. SCI., 52:884-892, 2011. (C) 2011 Society of Plastics Engineers