Amorphous silicon films doped with rare earth element Er fabricated with electron beam evaporation containing Er content up to about 10(21) cm(-3) were investigated employing the experimental methods of temperature dependence of d.c. conductivity, electron spin resonance (ESR) and optical bandgap E-opt measurements. We found that at 290 K < T < 330 K hopping conduction in Er impurity states near the Fermi level is predominant, and at 330 K < T < 500 K extended state conduction dominates due to electrons excited from the impurity states. An Er concentration of about 6.0 x 10(19) cm(-3) is a turning point of changing tendency for spin density N-s, peak-peak width Delta B-pp and line-shape factor I of ESR as a function of Er content. The optical gap of the films narrows with increasing Er content in the films from 1.68 eV to 0.40 eV. The results were partly explained on the basis of the partial compensation of Er atoms for dangling bonds Si-3(0).