The actual accelerating voltage in a scanning electron microscope (SEM) was determined using electron channeling patterns (ECPs). The technique involves selection of a set of high index lines. The properly chosen set of lines exhibits highly sensitive shifts as voltage is changed, allowing rapid SEM voltage calibration. The actual voltage is determined from a simple formula involving measurement of two distances on an ECP obtained from (100) silicon. Such calibrations were performed using both (100)Si and (100)GaAs crystals and the results were compared with voltage estimates from the high energy end of the continuous x‐ray spectrum from silicon. The ECP determination was accurate to about 0.1 keV for a nominal setting of 15 keV. This is comparable to the accuracy of the x‐ray technique when short (∼300 s) counting times are used.