Why Do MOSFETs Fail? The 6 Most Common Causes and How to Prevent Them
When a power MOSFET fails it usually shorts; it blows the fuse feeding the circuit or leaves heat behind. But the real question is: why did it burn? Because fitting a new one without finding the cause usually ends with that one burning too. The good news is that most MOSFET deaths come down to a few recurring reasons. In this article we cover the 6 most common causes with their symptoms and prevention.
First, a quick map
| Cause | Typical symptom | Prevention |
|---|---|---|
| Excess VGS | Gate-source short | Gate-source Zener / voltage limit |
| Overtemperature | Body burn, discoloration | Heatsink, derating |
| Voltage spike (VDS) | Drain-source breakdown | Snubber, TVS, layout |
| Slow switching | Overheating, efficiency loss | Gate driver, gate resistor |
| Gate oscillation | Erratic/sudden failure | Gate resistor, short trace |
| ESD | Sudden death during assembly | ESD protection, grounding |
1. Excess gate voltage (VGS)
The thin insulation layer between gate and source withstands around ±20 V in most MOSFETs. If noise, oscillation or wrong drive exceeds this limit, the insulation breaks down and the MOSFET is permanently damaged. Prevention: put a Zener diode between gate and source or keep the gate voltage in the safe range. If you use a logic-level MOSFET, choose the right VGS(th) class.
2. Overtemperature and insufficient cooling
In conduction, a MOSFET dissipates power through its on-resistance (RDS(on)) and heats up. If this heat isn't removed, the junction temperature exceeds its limit and the part fails. Prevention: enough copper area or a heatsink, choosing a part with low RDS(on), and a thermal-resistance calculation. Always apply derating for current and temperature; don't run it at the datasheet maximum.
3. Drain voltage spike (VDS spike)
When switching an inductive load like a motor, relay or coil, the inductance produces a high voltage spike when the current is suddenly cut. If this spike exceeds the MOSFET's VDS limit, the drain-source breaks down. Prevention: a flyback diode across the load, a snubber (RC) in parallel with the MOSFET and a TVS diode; plus a good PCB layout that keeps the power loop short.
4. Slow switching
At the moment of transition (neither fully on nor fully off), the MOSFET carries both voltage and current; high power is dissipated at that instant. The longer the transition takes, the more heat is released. The cause is usually weak drive. Prevention: use a gate driver that charges/discharges the gate quickly and account for the gate charge (Qg). A microcontroller pin can't drive a large MOSFET quickly and directly.
5. Gate oscillation
The parasitic inductance and capacitance at the gate leg can create an unwanted oscillation (ringing) at high speed. This oscillation both stresses the VGS limit and heats the MOSFET by switching it on and off uncontrollably. Prevention: put a small series gate resistor (for example a few to tens of ohms) between the gate and the driver, and keep the gate trace as short as possible.
6. Electrostatic discharge (ESD)
MOSFETs are sensitive to static electricity; an invisible discharge from your hand during assembly can break down the gate insulation. This death happens on the bench, before it's ever fitted to the circuit. Prevention: an antistatic wrist strap, a grounded work surface and keeping parts in antistatic packaging.
Common mistakes
- Replacing without finding the cause: the same fault burns the new MOSFET too; find the root cause first.
- Driving directly from an MCU pin: it creates slow switching and heating; a gate driver is needed.
- Skipping the gate resistor: it raises the risk of oscillation and VGS overshoot.
- No protection on an inductive load: without a flyback/snubber/TVS, a voltage spike breaks down the MOSFET.
- Running at maximum ratings: use without derating zeroes out the temperature and voltage margin.
Frequently asked questions
Does a MOSFET short or open when it fails?
It mostly shorts drain-source; that's why, when it fails, it blows the fuse or stresses the supply stage. You can confirm the short by measurement.
Which MOSFET failure is most common?
In practice, lack of heat/derating and voltage spikes on inductive loads are the two most common causes.
Does using a MOSFET instead of a BJT reduce failure?
If driven correctly, yes, but both have different weak points. For a selection comparison, see our MOSFET vs BJT article.
Conclusion
MOSFET deaths aren't random; gate voltage, heat, voltage spikes, slow switching, oscillation and ESD explain most of these failures. With the right driver, protection elements and derating, your MOSFET will be long-lived. You can review supplier offers for the MOSFETs and drivers you need with search and the comparison tool.