3SK123 MOSFET — Specifications & Equivalents

About the 3SK123

The 3SK123 is an N-channel MOSFET with a drain–source voltage (V_DS) rating of 18 V, a continuous drain current (I_D) of 0.025 A and an on-resistance (R_DS(on)) of 200 Ω. It can dissipate up to 0.2 W and is rated to a junction temperature of 125 °C. It is supplied in the TO131 package.

At a glance

• Type: N-channel MOSFET
• Max drain–source voltage (V_DS): 18 V
• Max continuous drain current (I_D): 0.025 A
• On-resistance (R_DS(on)): 200 Ω
• Power dissipation (P_D): 0.2 W
• Max junction temperature (T_J): 125 °C
• Package: TO131

Typical applications

With its 18 V drain–source rating the 3SK123 sits in the very-low-voltage class of switching MOSFETs, typically found in battery protection and power-path switching, point-of-load converters and logic-level load switching in portable devices.

At 0.025 A it is aimed at small-signal and light-load switching rather than power conversion.

On-resistance of 200 Ω is relatively high, so this part is better suited to low duty-cycle or low-current switching than to continuous high-current conduction.

Gate drive and switching notes

Keep gate–source voltage within the ±8 V maximum; exceeding it punctures the gate oxide and destroys the device permanently.

Choosing a replacement for the 3SK123

A drop-in substitute for the 3SK123 must be the same N-channel type and offer a drain–source rating of at least 18 V, a continuous drain current rating of at least 0.025 A and an on-resistance no higher than 200 Ω if efficiency and heat matter.

Mechanically, check the replacement against the TO131 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Where the application switches inductive loads or runs near the voltage limit, keep extra headroom rather than choosing a part that only just meets the original numbers.

Frequently asked questions

What is the 3SK123?

The 3SK123 is an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor). It is rated for 18 V drain-source and 0.025 A continuous drain current.

What is the maximum voltage of the 3SK123?

The 3SK123 has a maximum drain-source voltage (Vds) of 18 V. Treat this as an absolute maximum and design with margin, especially when switching inductive loads.

How much current can the 3SK123 handle?

It is rated for 0.025 A of continuous drain current, with power dissipation limited to 0.2 W. Real-world capability depends on your heatsinking and ambient temperature.

What is the on-resistance of the 3SK123?

On-resistance (Rds(on)) is 200 Ω. Multiply by the square of your load current to estimate conduction loss.

What package does the 3SK123 come in?

It is listed in TO131. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 3SK123?

No verified equivalents are listed yet. Choose a part of the same polarity that meets or exceeds every rating above and shares a compatible package and pinout.