phones, notebook computers, and the communications infrastructure that enables the Internet. As of 2010, the power MOSFET accounts for the majority (53%) of the power transistor market, followed by the IGBT (27%), then the RF amplifier (11%), and then the bipolar junction transistor (9%). Solid-state devices Classifications A power device may be classified as one of the following main categories (see figure 1): A two-terminal device (e.g., a diode), whose state is completely dependent on the external power circuit to which it is connected. A three-terminal device (e.g., a triode), whose state is dependent on not only its external power circuit, but also the signal on its driving terminal (this terminal is known as the gate or base). A four terminal device (e.g. Silicon Controlled Switch -SCS). SCS is a type of thyristor having four layers and four terminals called anode, anode gate, cathode gate and cathode. the terminals are connected to the first, second, third and fourth layer respectively. Another classification is less obvious, but has a strong influence on device performance: A majority carrier device (e.g., a Schottky diode, a MOSFET, etc.); this uses only one type of charge carriers. A minority carrier device (e.g., a thyristor, a bipolar transistor, an IGBT, etc.); this uses both majority and minority carriers (i.e., electrons and electron holes). A majority carrier device is faster, but the charge injection of minority carrier devices allows for better on-state performance. Diodes An ideal diode should have the following characteristics: When forward-biased, the voltage across the end terminals of the diode should be zero, no matter the current that flows through it (on-state). When reverse-biased, the leakage current should be zero, no matter the voltage (off-state). The transition (or commutation) between the on-state and the off-state should be instantaneous. In reality, the design of a diode is a trade-off between performance in on-state, off-state, and commutation. Indeed, the same area of the device must sustain the blocking voltage in the off-state and allow current flow in the on-state; as the requirements for the two states are completely opposite, a diode has to be either optimised for one of them, or time must be allowed to switch from one state to the other (i.e., the commutation speed must be reduced). These trade-offs are the same for all power devices; for instance, a Schottky diode has excellent switching speed and on-state performance, but a high level of