Abstract: A method of making a field-effect transistor is described in which first and second insulating layers are formed in crystalline material by ion implantation and, if necessary, annealing, further crystalline material being grown, if necessary, after the first layer has been implanted. Source and drain regions are defined in the material between the first and second layers, a layer of protective oxide is formed and metallization to form contacts for a gate region and the source and drain regions is deposited. Field-effect transistors made by the method are described and circuits containing such transistors can be separated by etching down to the first layer or by regions of amorphous material.