A simple but ultrasensitive method for measuring MOS gate currents down to the attoampere range has been developed. The new technique routinely measures oxide currents in conventional MOSFET structures arising from effects such as hot-electron emission, oxide leakage or tunneling at levels too low to be easily detected by previously available techniques. No FAMOS-type device is required. This technique was used to measure both channel and substrate hot-electron currents. Substrate hot-electron currents measured with the new technique were in excellent agreement with those measured directly. Copyright © 1980 by The Institute of Electrical and Electronics Engineers, Inc.