A semiconductor device comprises a semiconductor layer of a polycrystalline silicon thin film containing not more than 3 atomic % hydrogen atoms and having a surface unevenness of not more than 800 ANGSTROM at its maximum. It may also have an etching rate of 20 ANGSTROM /sec. when etched with a mixture of HF, HNO3 and glacial acetic acid (1:3:6).
