Biological macromolecules (such as proteins, DNA, and RNA) are the machinery of biological processes. Sensors enabling quantitative, real-time detection of these objects promise an enhanced understanding and management of disease and illness, with obvious application to medicine and public health. Ideally, these such biosensors would be useable in the field, at medical point of care, or even in vivo, all of which places where sample preparation would be minimal and use of labeling reagents (e.g., fluorescently labeled antibodies) not practical. In a collaboration between the Electronics Science and Technology Division and the Center for Bio/Molecular Science and Engineering we have developed a microelectronic biosensor capable of label-free detection of a variety of biological macromolecules. When fully realized and implemented as elements in an array format, this biosensor may enable low cost, simultaneous, real-time detection of thousands of target macromolecules from small sample volumes (10's of ?liters) or even in vivo. We describe here the construction and performance of an example sensor based on conventional siliconbased technology, as well as future applications.