Ultra-large scale integration, or ULSI for short, refers to the ability to position more than one million integrated circuits on a single computer chip. An integrated circuit is a circuit whose components are etched onto a slice of semiconductor material.

The ability to pack more integrated circuits onto a chip increases the computational power and speed of the computer or other machine in which the chip resides. The use of ULSI in a device permits operation at a lower voltage, lowers the power consumption and provides a higher speed of operation. Some of the devices that utilize ULSI technology are processors, scanners that convert printed information to coded data, semiconductor memory, semiconductors (such as the Metal Oxide Semiconductor Field Effect Transistor, or MOSFET), and the bipolar transistor, which amplifies analog and digital signals. The widely used Intel 486 and Pentium microprocessors--silicon chips that contain the computer's central processing unit--use USLI technology.

USLI is the largest type of integrated circuit. The other types rang in size from less than 100 circuits (small-scale integration) to between 100,000 and 1,000,000 (very-large scale integration, or VLSI). Operationally, the dividing line between VLSI and ULSI integrated circuits is often difficult to determine.