In short: Use a MOSFET below roughly 600 V or above ~50 kHz, where its resistive, fast, unipolar conduction wins; use an IGBT from about 650 V upward at lower switching frequencies, where its conductivity-modulated bipolar drift region beats the MOSFET's rapidly growing on-resistance.
Two switches, two different physics
A power MOSFET is a unipolar device: current is carried only by majority carriers (electrons in an n-channel part) through a channel and an n-type drift region. An IGBT bolts a MOSFET gate structure onto a p+ collector layer, so the same drift region is also flooded with minority carriers injected from the collector. That single extra junction explains almost every difference in the comparison below. If you have not yet seen the cell geometry, read our primer on power MOSFET structure first.
Think of the IGBT as a MOSFET driving the base of a wide PNP transistor. The MOSFET turns the device on cheaply with a voltage on the gate, while the PNP provides the low on-state drop of a bipolar transistor.
Voltage rating and the drift-region problem
Blocking voltage is set by the thickness and doping of the lightly doped drift region. Higher breakdown demands a thicker, more lightly doped layer, and for a unipolar device the specific on-resistance climbs roughly as VBR to the power 2.4 to 2.6. Doubling the rating costs about a 5x increase in RDS(on) per unit area.
Key fact: a 600 V silicon superjunction MOSFET may reach 40 mΩ in a TO-247, while a 60 V trench MOSFET reaches under 1 mΩ. The same die area at 1200 V in silicon would be hopeless, which is why 1200 V designs historically went to IGBTs.
In an IGBT the injected holes raise the carrier density in the drift region by orders of magnitude, collapsing its resistance. The on-state drop becomes a nearly constant VCE(sat) of about 1.5 to 2.2 V, largely independent of rating. That is why 1200 V, 1700 V and 3300 V modules are almost exclusively IGBT-based, and why silicon carbide MOSFETs are the real disruptors in that range today.
Conduction loss: resistor versus fixed drop
A MOSFET behaves like a resistor: P = ID,rms² × RDS(on). An IGBT behaves like a diode plus a small resistor: P ≈ VCE0·I + rCE·I². The two curves cross at a crossover current. Worked example: a 650 V MOSFET with RDS(on) = 50 mΩ at 125 °C (hot value, often 1.6-1.8x the datasheet 25 °C figure) drops 0.5 V at 10 A, but 2.5 V at 50 A. A 650 V IGBT drops about 1.7 V at both. Below roughly 30 A the MOSFET dissipates less; above it the IGBT wins.
Key fact: always use the 125 or 150 °C RDS(on) when comparing. The cold datasheet headline number flatters the MOSFET by up to 70 percent.
Switching speed and the tail current
A MOSFET turns off as fast as its gate can remove charge from Ciss and Cgd: typically 10 to 50 ns. Current falls to zero because there is no stored minority charge. The IGBT cannot do that. When the gate switches off, the MOSFET portion stops delivering electrons, but holes remain stranded in the drift region and must decay by recombination. The result is a slowly decaying tail current lasting 200 ns to several microseconds, during which the collector voltage is already high.
The tail energy Eoff is multiplied by frequency: at 100 µJ per pulse, 20 kHz costs 2 W per device, but 200 kHz costs 20 W, which is thermally unacceptable. Practical ceilings follow: IGBTs mostly operate at 5 to 30 kHz (fast "trench-FS" parts reach 50 to 100 kHz in soft-switching resonant stages), while Si MOSFETs reach several hundred kHz and GaN parts reach MHz.
Side-by-side summary
| Property | Power MOSFET | IGBT |
|---|---|---|
| Typical voltage range | 12 V to ~900 V (Si) | 600 V to 6.5 kV |
| On-state behaviour | Resistive, I²R | Fixed drop ~1.5-2.2 V plus small resistance |
| Turn-off | 10-50 ns, no tail | 100 ns knee + 0.2-several µs tail |
| Practical frequency | 50 kHz to MHz | 2 to ~30 kHz (up to 100 kHz soft-switched) |
| Body diode | Intrinsic (slow in high-voltage types) | None; needs co-packaged freewheel diode |
| Short-circuit tolerance | Weaker, small die | Rated 5-10 µs in motor-drive parts |
| Temperature coefficient | Positive (easy paralleling) | Positive at high current, negative at low |
Where each one wins in real products
- MOSFET: server and laptop VRMs, USB-C chargers, LLC and flyback converters, synchronous rectification, DC-DC converters under 500 V, motor drivers for e-bikes (48 V).
- IGBT: traction inverters in older EVs and railways (650-1700 V), industrial motor drives and VFDs, welding machines, UPS inverters, induction cookers, solar string inverters.
- Overlap zone (400-900 V): on-board EV chargers and PFC stages, where superjunction MOSFETs, GaN and SiC increasingly displace IGBTs because they allow smaller magnetics at higher frequency.
Key fact: a quick selection rule used in interviews is "below 250 V pick a MOSFET, above 1 kV pick an IGBT or SiC, and in between let switching frequency and load current decide."
Simulating the trade-off
Designers rarely trust datasheet figures alone. Cadence PSpice and Synopsys SaberRD ship behavioural IGBT models that capture tail current, while Siemens Simcenter and LTspice-style tools model MOSFET gate charge. For die-level work, Synopsys Sentaurus TCAD simulates carrier injection and lifetime control, letting engineers tune the tail against VCE(sat), which is the central trade-off of IGBT design. Teams building such power stages commonly lean on partners like Avecas design services for analog and mixed-signal implementation.
Gate drive also differs: IGBT gates typically swing +15 V / -8 V to hold the device off against dV/dt, while logic-level MOSFETs run from 5 to 10 V. Learn the fundamentals on a structured path at ChipXpert training, and see how conduction and switching losses combine in our guide to switching loss calculation.
Frequently asked questions
Can an IGBT replace a MOSFET in a 12 V design?
No. The roughly 1.5 V or higher saturation drop would waste over 10 percent of the supply, while a 5 mΩ MOSFET drops millivolts. IGBTs only pay off at high voltage.
Why does an IGBT need a separate freewheel diode?
The p+ collector junction blocks reverse current, so there is no intrinsic body diode. Inverters therefore co-package a fast-recovery diode antiparallel to each IGBT.
Is SiC MOSFET a MOSFET or an IGBT replacement?
Both. It is a unipolar MOSFET with a wide-bandgap drift region, so it reaches 1200 V with low RDS(on), no tail current and high frequency, directly displacing IGBTs in EV inverters.
What is the crossover frequency between them?
There is no universal number, but for 600 V class hard-switched converters it typically falls near 20 to 50 kHz, depending on current, temperature and cooling.
Want to master device physics and power-stage design with hands-on simulation? Explore the analog and power electronics tracks in our CourseTron courses.