This article gives a quantitative analysis of electron photoemission yield from N+-type and P+-type substrates of MOS structures. Based on this analysis, a method is presented to estimate both the scattering length, ℓ, of electrons in the image force potential well and of photoelectron escape depth, xesc, from the semiconductor substrate. This method was used to estimate the scattering length and the escape depth from the substrates of Al-SiO2-Si (N+-type and P+-type) structures. It was found that for N+-type substrate structures the scattering in the image force potential well has a dominating influence on the photoemission yield while for P+-type substrate structures both the scattering in the image force potential well and the photoemission from the subsurface regions of the photoemitter play important roles. It was found that the scattering length in the image force potential well was equal to ℓ = 6.7–6.9 nm for structures on both N+ and P+ substrates, produced in the same processing conditions. For structures on P+ substrates, the escape depth was found to be equal to xesc = 8–9 nm. The scattering length, ℓ, determined in this study is considerably larger than the one reported previously (ℓ = 3.4 nm) for similar MOS structures. The escape depth xesc determined in this study is also considerably larger than the escape depth determined previously (xesc = 1.2–2.5 nm) for the external photoemission from uncovered silicon surfaces into vacuum.