We have investigated the degradation effects of ozone exposure on organic field-effect transistors based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene as the organic semiconducting channel layer, as well as on thin films of this widely used, high-mobility, small molecule semiconductor. Electrical I-V measurements showed a loss of transistor characteristic behavior. We present ¹H Nuclear Magnetic Resonance (NMR) spectroscopy results as well as X-ray Photoemission Spectroscopy (XPS) and Fourier Transform Infrared (FTIR) spectroscopy measurements showing the oxidation of the parent molecule, from which we suggest various possible reaction paths.