The safe operation area (SOA) of a device provides the current and voltage limits the device must be able to handle to avoid destructive failure. Typical SOA for a MOSFET device is shown in Fig (a). The maximum current limit while the device is on is determined by the maximum power dissipation,

$P_{\mathrm{diss}, \mathrm{ON}}=I_{\mathrm{DS}(\mathrm{ON})} R_{\mathrm{DS}(\mathrm{ON})}$

As the drain-source voltage starts increasing, the device starts leaving the on-state and enters the saturation (linear) region. During the transition time the device exhibits large voltage and current simultaneously.

At higher drain-source voltage values that approach the avalanche breakdown it is observed that power MOSFET suffers from a second breakdown phenomenon. The second breakdown occurs when the MOSFET is in the blocking state (off) and a further increase in $V_{DS}$ will cause a sudden drop in the blocking voltage. The source of this phenomenon in MOSFET is caused by the presence of a parasitic n-type bipolar transistor as shown in Fig (b).

The inherent presence of the body diode in the MOSFET structure makes the device attractive for applications in which bidirectional current flow is needed in the power switches.

Today’s commercial MOSFET devices have excellent high operating temperatures. The effect of temperature is more prominent on the on-state resistance as shown in Fig (c).

As the on-state resistance increases, the conduction losses also increase. This large $V_{DS(OW)}$ limits the use of the MOSFET in high-voltage applications.

The use of silicon carbide instead of silicon has reduced $V_{DS(OW)}$ many fold. As the device technology keeps improving, especially in terms of improved switch speeds and increased power handling capabilities, it is expected that the MOSFET will continue to replace BJTs in all types of power electronics systems.