We have investigated the deterioration of field effect transistors based on twodimensional materials due to irradiation with swift heavy ions. Devices were prepared with exfoliated single layers of MoS 2 and graphene, respectively. They were characterized before and after irradiation with 1.14 GeV U 28+ ions using three different fluences. By electrical characterization, atomic force microscopy and Raman spectroscopy we show that the irradiation leads to significant changes of structural and electrical properties. At the highest fluence of 4 × 10 11 ions/cm 2 , the MoS 2 transistor is destroyed, while the graphene based device remains operational, albeit with an inferior performance. * electronic address: marika.schleberger@uni-due.de