A method for manufacturing a semiconductor device includes steps of: forming a first epitaxial film on a silicon substrate; forming a trench in the first epitaxial film; and forming a second epitaxial film on the first epitaxial film and in the trench. The step of forming the second epitaxial film includes a final step, in which a mixed gas of a silicon source gas and a halide gas is used. The silicon substrate has an arsenic concentration defined as α. The second epitaxial film has an impurity concentration defined as β. The arsenic concentration and the impurity concentration has a relationship of: α≦3×1019×ln(β)−1×1021.