A process separates a main body of a semiconductor substrate from a functional layer. The method includes the steps of implanting ions into a semiconductor substrate through a top surface of the semiconductor substrate to form an ion damage layer underneath the top surface of the semiconductor substrate. After the ions are implanted into the semiconductor substrate, a functional layer is formed on the top surface of the semiconductor substrate. The main body of the semiconductor substrate is then separated from the functional layer. The method also includes forming the functional layer on the semiconductor substrate after ion implanting and then separating the functional layer from the main body of the substrate at the ion damage layer. This method avoids bonding in SOI and can thus reduce process steps and cost.