The MOSFET is constructed in a different way compared to the point-contact transistor. First of all, the semiconducting material has been replaced. Instead of germanium, silicon is being used. Silicon is less expensive and has physical properties better suited for today's transistors. The MOSFET is made up of silicon layers with different kinds of doping. The electrodes in this type of transistor are called source, drain and gate. The current flowing from source to drain is controlled with the charge of the gate, which is constructed of a highly conductive material, often polysilicon. To function properly this gate-electrode needs to be insulated from the rest of the transistor. This insulation is made possible by a layer of silicon oxide that surrounds the gate.