Transistors are solid-state electronic devices used to control the flow of electricity in electronic equipment and consist of a semiconductor material with at least three electrodes for connection to a circuit. Common types include BJT transistors, RF transistors, Darlington transistors, and MOSFET transistors. Common brands include International Rectifier, Uxcell, Amico, and Sunkee. Each type of transistor has properties that suit it for specific tasks. General purpose and bipolar transistors are available individually and in assortments. Kits are available to build demonstration projects, such as radios, and may include additional electronic components. When choosing a transistor, consider the voltage and current requirements of the application.