The boron concentration profile in silicon epitaxial wafers grown under atmospheric pressure was investigated in two types of epitaxial reactors. Transport phenomena are studied both by numerical calculations or by a gas flow visualization technique. The difference between the measured boron concentration profile and the calculated one using Fick’s law was assumed to be due to autodoping. In epitaxial wafers grown at temperatures lower than 1273 K on a p-type substrate in a single-wafer horizontal reactor which has no recirculation of gas, the boron concentration profile changed abruptly at the interface between the epitaxial film and the substrate since the profile is formed only due to solid-state diffusion. In contrast, in a pancake reactor having large recirculation of gas, a gradual change in the boron concentration profile was observed due to autodoping via the gas phase. In conclusion, large amounts of recirculation of gas in an epitaxial reactor should be avoided to obtain an abrupt boron concentration profile.