Loading…
SOT-23 · BSS138
ActiveMOSFET (N-Channel)
BSS138
onsemi · SOT-23 · MOSFET (N-Channel)
Price on Request
Get a competitive quote within 24 hours. Volume discounts available. Shenzhen stock ships in 1-2 business days.
Overview
The BSS138 is onsemi's 50 V N-channel logic-level MOSFET in the compact SOT-23 package, rated for 200 mA continuous drain current with 3.5 Ω max on-resistance at Vgs=10 V. It is the direct competitor to Nexperia's 2N7002 and shares the same pinout, package and general application space — low-power switching, level shifting, and load switching where currents stay under 200 mA.
The BSS138 has slightly lower gate threshold (0.8-1.5 V vs 2N7002's 1-2.5 V), which means it turns on more reliably from 3.3 V logic. This makes it the preferred choice for modern low-voltage designs where every millivolt of gate overdrive matters. On the downside, Rds(on) is higher (3.5 Ω vs 2.4 Ω) and continuous current is lower (200 mA vs 300 mA), so for higher-current applications the 2N7002 wins.
Package is standard SOT-23 with pinout G-S-D (pin 1 = Gate, pin 2 = Source, pin 3 = Drain). Gate oxide is protected by an internal zener clamp to ±20 V.
Fully second-sourced across onsemi (BSS138LT1G), Nexperia (BSS138), Diodes Inc (BSS138-7-F), Vishay, STMicroelectronics, and many Asian vendors. All are pin-and-function compatible.
Common uses: I²C and SPI level shifting between 1.8 V / 2.5 V / 3.3 V / 5 V domains, load switches for LEDs and small motors, signal muxing, ESD steering on low-speed data lines, and battery management.
Our Shenzhen stock: onsemi BSS138LT1G (SOT-23) MOQ 3,000 pcs on reel or 100 pcs loose.
Key Features
- 50 V drain-source, 200 mA continuous drain current
- Low gate threshold (0.8-1.5 V) for 3.3 V and 1.8 V logic
- Internal ±20 V gate zener protection
- Compact SOT-23 with industry-standard pinout
Typical Applications
- I²C and SPI bus level shifting
- Low-current load switching (LEDs, sensors, small relays)
- Signal muxing and analog switching
- Battery management and reverse-polarity protection
- ESD steering on low-speed data lines
Specifications
- Channel Type
- N-Channel
- Drain-Source Voltage
- 50 V
- Continuous Drain Current
- 200 mA
- Rds(on) Max
- 3.5 Ω
- Gate Threshold Voltage
- 0.8 to 1.5 V
- Power Dissipation
- 225 mW
- Operating Temperature
- -55 to 150 °C
- Mounting Type
- Surface Mount
- RoHS
- Compliant
Procurement Tips
For level-shifting applications, consider the dedicated TXS0108E or TXB0104 bidirectional translators — they handle open-drain I²C and push-pull SPI automatically, eliminating the resistor-and-MOSFET network.
Frequently Asked Questions
BSS138 vs 2N7002 — which should I choose?
For 3.3 V or 1.8 V logic systems, BSS138 (lower Vgs(th), turns on more reliably). For 5 V logic and currents up to 300 mA, 2N7002 (lower Rds(on), higher current rating). They are functionally interchangeable in most circuits under 100 mA.
Can BSS138 handle 12 V load switching?
Yes — 50 V rating gives you 4× margin for 12 V rails including inductive spikes. Current must stay under 200 mA continuous; for higher currents use SI2302 (2.8 A) or AO3400 (5.7 A).
Why is my BSS138 getting hot at only 150 mA?
Check gate drive voltage. At Vgs=3.3 V, Rds(on) is around 5 Ω (not the 3.5 Ω datasheet value at Vgs=10 V), so dissipation is 150 mA² × 5 Ω = 112 mW — noticeable in SOT-23. If you need more current, use SI2302 or add a proper gate driver to reach Vgs=5 V.
Does BSS138 need a gate pull-down resistor?
Yes, strongly recommended. The gate is capacitive and can float during MCU reset or deep sleep. A 100 kΩ gate-to-source pull-down keeps the MOSFET off. Also add a 100 Ω series gate resistor to damp ringing.
Is BSS138 counterfeit-prone?
Moderately. Genuine onsemi parts have laser-etched "BSS138" or code "M4N", matte tin leads, consistent weight. Fakes are often remarked lower-voltage MOSFETs that fail above 20 V. Test by applying 30 V drain-source with the gate off — genuine BSS138 blocks; fakes break down.
MOQ and lead time?
MOQ 3,000 pcs on reel for onsemi BSS138LT1G, or 100 pcs loose. onsemi authorized 8-16 weeks; Shenzhen stock 1-2 days.
Alternatives & Equivalents
View full cross-reference table →Need BSS138 pricing and availability?
Submit an RFQ — we reply within 24 hours with stock, pricing, lead time and packaging options.
Request a Quote →