Part of the Day · BSS138 — SOT-23 N-channel MOSFET (marking SS)

Part of the Day · 2026-10-23

An SMD small-signal N-channel MOSFET driven at logic level. It is often found in 3.3V ↔ 5V level-shifter modules and small load switching, and is marked SS.

Actual size

↓ Actual size, left edge aligned to 0 on the ruler

One ruler tick = 1mm. On PC this is actual size on a 24-inch FHD monitor at 100% zoom; on iPhone it adjusts automatically. For other screens, use “Calibrate ruler” below.

Enlarged (SOT-23 · top view · approx. 20×)

Pins 1 Gate · 2 Source · 3 Drain

Package SOT-23 · Marking SS

Key specifications

Values are from the onsemi datasheet.

Marking and pins

Marking code SS · Pins 1 Gate · 2 Source · 3 Drain

Typical uses

• Low-voltage, low-current switching — e.g. small servo motor control
• Power MOSFET gate driver, logic level translation

Companion & similar parts

• 2N7002 — Similar SOT-23 N-channel MOSFET (60V, 300mA) — threshold voltage and on-resistance differ, check before substituting

Marking code SS follows onsemi. BSS138 parts from other makers may use different codes, so check the Marking table in that maker's datasheet.