A method of manufacturing a semiconductor wafer, the method comprising: providing a base wafer comprising a semiconductor substrate; preparing a first monocrystalline layer comprising semiconductor regions; preparing a second monocrystalline layer comprising semiconductor regions overlying the first monocrystalline layer; and etching portions of said first monocrystalline layer and portions of said second monocrystalline layer as part of forming at least one transistor on said first monocrystalline layer.