Solid‐phase epitaxial Si layers of uniform thickness have been grown at 400–500 °C by transport of Si atoms from an amorphous Si film through an Al film deposited on ⟨100⟩ single crystal or polycrystallinen‐type Si substrates. The epitaxial Si layers are stronglyptype due to Al doping, and good rectifying junctions are formed between these layers and the substrates. Solar cells with conversion efficiencies at AM1 of 10.4 and 8.5% have been fabricated on ⟨100⟩ Si and polycrystalline Si substrates, respectively, without the use of an antireflection coating or back‐surface field structure.