ABSTRACTLabel-free, real-time, parallel and complementary electrical detection of proteins is demonstrated by p-type and n-type silicon nanowire field-effect transistors in the same arrays. Composed of hundreds of individually electrically addressable nanowire devices with highly sensitive and reproducible performances, these nanowire arrays can be controllably modified by monoclonal antibodies, and show discrete conductance changes characteristic of highly selective binding and unbinding of target proteins, such as prostate specific antigens (PSA), thus providing a general and powerful platform for high-throughput real-time parallel detection and rapid screening of libraries of biomolecules. Studies show that the PSA proteins can be routinely detected at femtomolar concentrations with high selectivity, and simultaneously incorporation of both p-type and n-type silicon nanowire devices enable discrimination against false positive/negative signals. The integrated complementary nanowire sensor arrays open up substantial opportunities for diagnosis and treatment of complex diseases such as cancer, detection of biological threats, and fundamental proteomic and biophysical studies.