Researchers have developed a way to see through silicon wafers, which among other things offers a powerful new tool for probing computer chips for tiny manufacturing defects. To prove the method, the team beamed patterns of radiation onto a 115-micrometer-thick wafer of silicon that temporarily enabled electrons to flow within the material, which is normally a semiconductor. While conductive, the silicon was transparent to terahertz radiation. (“Terahertz” refers to trillions of cycles per second; such radiation lies between microwave and infrared radiation and has wavelengths between 150 nanometers and 1.5 millimeters.) Then, the researchers measured the radiation bouncing back through the silicon to discern objects or features present on the back side of the wafer (example, above, shows a 2-by-2-millimeter portion of a circuit). Using their technique, the scientists were able to spot circuit defects as small as 8 micrometers across (or about half the diameter of the finest human hair), they report online today in Science Advances. In the short term, the most likely use for the technique might be quality control in factories making computer chips. But in the longer term, the technique could be used to scrutinize thin sections of biological tissue for signs of disease, the researchers suggest. Terahertz imaging wouldn’t be useful to probe thicker slices of tissue or image body parts, for example, because water—a major component of all living tissue—strongly absorbs those wavelengths of radiation and thus blocks the technology’s ability to see into or through these objects.