A photoexcitation technique for the direct measurement of metal‐oxide‐semiconductor (MOS) flat‐band voltage is described. The principle consists of generating excess carriers in the semiconductor space‐charge region by infrared pulses as a function of potential applied across the MOS capacitor and utilizing the fact that the current pulses induced in the external circuit become identically zero when the applied voltage is equal to the flat‐band voltage. Experimental results are presented for MOS on silicon substrates.