This invention is directed to form a homogeneous film in a via hole formed in a semiconductor device using Bosch process. The via hole that penetrates through a predetermined region in a semiconductor substrate is formed by etching the semiconductor substrate from one of its surface to the other by the Bosch process using a mask layer as a mask. Next, the mask layer is removed. Then, scallops are removed by dry etching to flatten a sidewall of the via hole. Following the above, an insulation film, a barrier layer and the like are formed homogeneously in the via hole.