A semiconductor device production method includes performing trench etching to form a trench in a thickness direction of a semiconductor layer so that both of a first pattern portion and a second pattern portion whose side walls face each other across the trench are formed. In the trench etching, the semiconductor layer is etched and removed while a protective film is formed on a surface of the semiconductor layer, and the trench etching is performed so that the first pattern portion and the second pattern portion are configured to have a same potential or a same temperature during the trench etching.