The study of electrical transport in biomolecular materials is critical to our fundamental understanding of physiology and to the development of practical bioelectronics applications. In this study, we investigated the electronic transport characteristics of Shewanella oneidensis MR-1 nanowires by conducting-probe atomic force microscopy (CP-AFM) and by constructing field-effect transistors (FETs) based on individual S. oneidensis nanowires. Here we show that S. oneidensis nanowires exhibit p-type, tunable electronic behavior with a field-effect mobility on the order of 10(-1) cm(2)/(V s), comparable to devices based on synthetic organic semiconductors. This study opens up opportunities to use such bacterial nanowires as a new semiconducting biomaterial for making bioelectronics and to enhance the power output of microbial fuel cells through engineering the interfaces between metallic electrodes and bacterial nanowires.