Arsenic doping by ion implantation and thermal annealing of the BaSi2 epitaxial films grown on Si(111) substrates has been studied. Raman spectroscopy shows that a structural change can occur by annealing at 500 degrees C after As implantation with as high dose as 1.0 x 10(15) cm(-2). This structural change is shown to result in the formation of an altered layer after annealing at the surface by cross-sectional scanning electron microscopy. Secondary ion mass spectroscopy reveals that the altered layer contains a significant amount of O atoms. With the altered layer present, average electron density up to 6.0 x 10(19) cm(-3) has been realized, which is revealed by the Hall measurement. On the other hand, without the altered layer, high resistance of the BaSi2 layer prevented the electrical characterization. Current path is discussed by theoretically calculating the band alignment and resistance, and possible highest electron density without the altered layer is extracted to be less than 2 x 10(17) cm(-3). (C) 2014 Elsevier B.V. All rights reserved.