A semiconductor device has active regions with different conductivity types. A substrate has a PMOS region and an NMOS region. A first active region is in the PMOS region. A second active region is in the NMOS region. A semiconductor layer is on the first active region. A first gate electrode crosses the first active region and extends on the semiconductor layer. A second gate electrode is on the second active region. An upper end of the first active region extends to a level lower than an upper end of the second active region. A lower end of the first active region extends to a level lower than a lower end of the second active region.