The probability of hot-hole injection has been measured both on metal nitride-oxide silicon (MNOS) and metal-oxide-semiconductor (MOS) structures in the case where the silicon electric field is one dimensional and normal to the interface. The experiment uses the effect of optically induced hot carrier injection as proposed by Ning et al. [J. Appl. Phys. 48, 286 (1977)]. In the case of MNOS structures, the hot-hole injection currents can be readily measured because the Si-Si3N4 interface barrier is lower than the Si-SiO2 interface barrier. Measurements on MOS structures were carried out using heavily doped silicon. The measurements have been interpreted using the lucky carrier model with some modifications: the hot-hole mean-free path has been found equal to 41±5 Å in the case of MOS structures. Taking into account the accuracy of the measurements, this value is compatible with the value derived in the case of MNOS structures and also with the value derived from ionization measurements.