The IMFP of electrons is a fundamental material parameter of surface analysis by AES, XPS, EPES and EELS. In surface analysis calculated IMFP values are used. Their experimental determination is rather difficult The IMFP of amorphous Ge and polycrysralline Si was determined by comparing rhe elastic peak inrensiry ratios with electrolytic Ni reference sample of 1 nm surface roughness, achieved by dedicated Ar+ ion bombardment cleaning and examined by STM. Experimental results obtained with a hemispherical analyser type ESA 31 developed by ATOMKI Debrecen have been evaluated by Monte Carlo analysis, based on Jablonski's differential elastic scattering cross sections and elaborated for the HSA analyser angular window. Due to the 5 x 1O-5 energy resolution of the ESA 31 no spectrometer correcrion was needed. The ratio of the background to the elastic peak was < 1% at 4 keV. The energy range was extended to 5 keV using Ashley's IMFP data. Reasonable agreement was found with our previous CMA experimental results in the overlapping energy range and with Ashley. They exhibit systematically higher values by 15-20%. EPES proved to be an efficient tool for IMFP measurements.