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A new type of integrated circuit that flashes with light as it routes electric currents here and there might have what it takes to boost computer speeds. Researchers from the University of California, San Diego, report they have built the first transistors (the building blocks of integrated circuits) that carry information not as electrons but as excitons—pairs of positive and negative charges created by shining light onto electrons in a semiconductor crystal, which leaves a positively charged "hole". Transistors switch the flow of electrons on or off, but to transmit such an electrical current through, say, a fiber-optic cable, a device has to convert the signal into light, which takes additional time and limits the overall speed of circuits used in telecommunications relays. Excitons could potentially cut this lag time because they flow like electrons but emit light when the electron–hole pair fuses back together. Researchers crafted a device from the semiconductor gallium arsenide that isolated electrons from holes until its transistors finished switching, then let the pairs come back together to produce light, as in this image. Writing in Science, the group reports that exciton transistors were as fast as the electron kind, although they only worked below –390 degrees Fahrenheit (about 40 kelvins). They say different semiconductors might work at warmer temperatures.