An SOT (Small Outline Transistor) package is a small, plastic, surface-mount package with gull-wing leads on two sides, used for transistors, diodes, voltage references, and small regulators. The SOT family spans from the 3-lead SOT-23 up through tabbed power packages like SOT-223. This guide gives the real dimensions, the JEDEC and manufacturer names that map to each one, thermal numbers that decide how much power you can actually dissipate, and a decision path for picking the right SOT package type.
Key takeaways
- SOT-23 is the anchor at 0.95 mm pitch and a 2.9 × 1.3 mm body; the family shrinks it (SC-70, SOT-523) or adds a heat tab (SOT-89, SOT-223).
- “SOT” appears in two unrelated numbering systems. The industry names (SOT-23, SOT-89, SOT-223) are one thing; NXP/Nexperia’s internal SOTxxxx codes are another, and they cover every package type.
- SOT-1123 is not a transistor package. It is an NXP 324-ball BGA (HBGA324) — proof that high SOTxxxx numbers encode registration order, not size.
- The tab is the whole story for power. A plain SOT-23 handles a few hundred milliwatts; a SOT-223 with copper pour handles over a watt.
- Pin count changes the body. A SOT-23-5 is 1.6 mm wide, not the 1.3 mm of a SOT-23-3 — a footprint trap.
- Package name is a hint, the drawing is the contract. Verify pinout and dimensions against the specific datasheet every time.
What “SOT” actually means — and the two numbering systems
SOT stands for Small Outline Transistor. The name dates to the early surface-mount era, when the 3-lead SOT-23 was introduced to replace the through-hole TO-18 and TO-92 transistors; the earliest variant, SOT-23-3, is registered by JEDEC as TO-236AB. Physically, an SOT is a molded-plastic body with gull-wing leads on the two long sides, sometimes with a third structural feature — an exposed metal tab or die pad — for heat.
Here is the part that trips up sourcing and BOM work. There are two different things both spelled “SOT.”
The first is the industry/JEDEC-style family: SOT-23, SOT-89, SOT-143, SOT-223, and the SC-70-class shrinks. In this system the number loosely tracks a registered outline, and the same shape carries many aliases across vendors.
The second is a manufacturer internal code. NXP and Nexperia assign a unique SOTxxxx number to every package outline they use — and not just transistors. In that registry the numbers are handed out roughly in the order packages were registered, so a high number tells you when it was added, not how big it is or what type it is. That is why NXP’s SOT1123 is an HBGA324 — a plastic, thermally-enhanced 324-ball ball-grid-array with a heatsink (per NXP’s SOT1123-1 outline drawing), while other high numbers in the same system, such as Nexperia’s SOT8009 and SOT1215, are ultra-thin leadless packages with side-wettable flanks. Same numbering system; a BGA, a leadless chip-scale part, and a transistor all coexist in it.
So a keyword like “SOT-23 through SOT-1123” mixes the two systems. There is no size ladder of transistor packages running up to 1123. If you see a SOTxxxx code on an NXP or Nexperia datasheet, treat it as a lookup key into their package tables, not as a size class.
[IMAGE 1: Side-by-side scale drawing of SOT-23, SC-70, SOT-89, and SOT-223 on a PCB with pitch and body dimensions labeled | alt: “SOT package types compared to scale: SOT-23, SC-70, SOT-89, and SOT-223 with pitch and body size labels”]
The SOT family at a glance
The table below lists nominal figures for common low-pin-count parts. Body dimensions are length × width × height excluding leads unless noted; always confirm against the device datasheet and its referenced outline.
| Package | Also known as | Leads | Pitch | Body (L×W×H) | Typical use |
| SOT-23-3 | TO-236AB, SC-59, SOT-346 | 3 | 0.95 mm | 2.9 × 1.3 × 1.0 mm | Signal transistors, diodes, references |
| SOT-23-5 | SOT-25, SC-74A, MO-178AA | 5 | 0.95 mm | 2.9 × 1.6 × 1.1 mm | Op-amps, small logic, LDOs |
| SOT-23-6 | SOT-26, SC-74, MO-178AB | 6 | 0.95 mm | 2.9 × 1.6 × 1.1 mm | Dual/triple devices, converters |
| SOT-323 | SC-70, UMT3 | 3 | 0.65 mm | 2.0 × 1.25 × 0.95 mm | Space-constrained signal parts |
| SOT-353 | SC-70-5, SC-88A | 5 | 0.65 mm | 2.0 × 1.25 × 0.95 mm | Small logic, references |
| SOT-363 | SC-88, SC-70-6 | 6 | 0.65 mm | 2.0 × 1.25 × 0.95 mm | Dual transistors, ESD arrays |
| SOT-523 | SOT-416, SC-75A, SC-90 | 3 | 0.50 mm | 1.6 × 0.8 × 0.6 mm | Ultra-small signal devices |
| SOT-553 | — | 5 | 0.50 mm | 1.6 × 1.2 × 0.6 mm | Ultra-small multi-lead |
| SOT-89 | TO-243, MPT3 | 3 (+tab) | 1.5 mm | 4.5 × 2.5 × 1.5 mm | Medium-power transistors, small LDOs |
| SOT-143 | TO-253, SOT-23-4 | 4 | 1.9 mm | 2.9 × 1.3 × 1.0 mm | Dual devices, RF, one wide lead |
| SOT-223 | TO-261AA | 4 (+tab) | 2.3 mm | 6.5 × 3.5 × 1.65 mm | LDO regulators, power devices |
Two family notes. A TSOT-23 (“thin” SOT-23) is the same footprint with reduced seated height for low-profile designs. And the leadless end of the family — Nexperia’s SOT8009-class parts and similar — drops gull-wing leads entirely for side-wettable-flank terminations, which is why those carry high internal codes rather than “SOT-23” names.
Signal packages: SOT-23 and its shrink path
For low-power switching, biasing, and reference work, the SOT-23-3 is the default. It carries no heat-spreading feature, so its usable dissipation sits in the low hundreds of milliwatts, but for a signal transistor that is plenty.
When you need more connections, the family keeps the 0.95 mm pitch and adds leads: SOT-23-5 and SOT-23-6 share a footprint, and the 6-lead land pattern will accept the 3- and 5-lead parts. Watch one detail — the multi-lead SOT-23-5/-6 body is 1.6 mm wide versus the 3-lead part’s 1.3 mm, so the footprints are not drop-in identical to a SOT-23-3.
When board area is the constraint, step down in size rather than up in leads. The SC-70 family (SOT-323/-353/-363) holds a 2.0 × 1.25 mm body at 0.65 mm pitch, and the SOT-523/SOT-416 shrinks further to roughly 1.6 × 0.8 mm at 0.5 mm pitch. Each step trades hand-assembly ease and thermal headroom for density.
One recurring hazard: SOT-23 pinouts are not standardized across parts. Base/emitter/collector or gate/drain/source assignments vary by device, so the schematic symbol and footprint must be checked against the specific datasheet before layout.
Power packages: SOT-89 and SOT-223 — the tab changes everything
Two members of the family exist specifically to move heat. The SOT-89 adds a die pad and an enlarged center lead that acts as a heat spreader into the board copper; JEDEC registers it as TO-243. The SOT-223 goes further with a large exposed tab and a 6.5 × 3.5 mm body (JEDEC TO-261AA), which is why it dominates small LDO regulators.
The mechanism is copper coupling. A leaded SOT-23 relies almost entirely on convection from a tiny plastic body. A SOT-89 or SOT-223 tab, soldered to a copper pour, conducts heat into the board and turns the PCB into the heatsink. That single difference is worth several times the dissipation, as the numbers below show.
Thermal reality: what you can actually dissipate
Package choice is a thermal decision as much as a size one. The table below uses the same device family measured in different packages, so the numbers are comparable rather than cherry-picked.
| Device (same family) | Package | θJA (junction-to-ambient) | Rated dissipation |
| BC817 | SOT-23 | 500 K/W | ~250 mW |
| BC817W | SOT-323 (SC-70) | 625 K/W | 200 mW |
| BC337 (reference) | TO-92 (through-hole) | 200 K/W | 625 mW |
| AMS1117 | SOT-89 | 225 °C/W | — |
| AMS1117 | SOT-223 | 150 °C/W | ~600 mW – 1.2 W |
| AMS1117 | TO-252 (DPAK, reference) | 125 °C/W | ~2.2 W |
Sources: the SOT-23/SC-70/TO-92 figures are from Nexperia’s BC817 series datasheet; the SOT-89/SOT-223/TO-252 figures are from the AMS1117 datasheet. Note the direction: the smaller SC-70 runs hotter than SOT-23 for the same die (625 vs 500 K/W), and the tabbed SOT-223 beats the smaller-tab SOT-89 (150 vs 225 °C/W). K/W and °C/W are numerically identical.
The SOT-223 number is also copper-dependent, which competitors rarely mention. JEDEC’s 51-3/51-7 test board for SOT-223 uses a defined 4 × 4 mm copper area (per Richtek’s application note AN044); on a real board, θJA for a SOT-223 LDO typically lands near 60 °C/W with modest copper and drops to about 35–40 °C/W with a 1 cm² pour under the tab.
Worked example. Run an AMS1117-3.3 at 800 mA from a 5 V rail. Dissipation is (5 − 3.3) × 0.8 = 1.36 W. At θJA = 60 °C/W in a 40 °C ambient, junction temperature rises to 40 + (1.36 × 60) ≈ 122 °C — right against the 125 °C limit. Add the 1 cm² copper pour to reach θJA ≈ 38 °C/W and the junction drops to about 40 + (1.36 × 38) ≈ 92 °C, a comfortable margin. Same part, same current; the copper is what keeps it alive.
[IMAGE 2: SOT-223 land pattern with a 1 cm² copper pour under the tab, annotated with heat-flow arrows | alt: “SOT-223 footprint with copper pour under the exposed tab showing thermal path into the PCB”]
Decoding a package name or suffix
SOT parts collect aliases because three naming authorities describe the same shape. Use this map to resolve them.
| Industry name | JEDEC | JEITA / EIAJ (SC-) | Common vendor codes |
| SOT-23-3 | TO-236AB (TO-236AA) | SC-59 | SMT3, UMT3, MPAK, S-Mini |
| SOT-23-5 / -6 | MO-178AA / AB | SC-74A / SC-74 | SOT-25 / SOT-26, TSOP-5/-6 |
| SOT-323 | — | SC-70 | UMT3, SC-70-3 |
| SOT-363 | — | SC-88 | SC-70-6, UMT6 |
| SOT-89 | TO-243 | — | MPT3 (ROHM) |
| SOT-223 | TO-261AA / TO-261-4 | — | — |
A few rules make this manageable. The trailing digit in “SOT-23-n” is the pin count, not a new package — SOT-23-5 is a 5-lead SOT-23. Calling it “SOT-25” or “SOT-26” is common shorthand but not the registered name. When a datasheet lists both an industry name and a JEDEC TO-/MO- number, the JEDEC number is the precise one to match a footprint against, because the marketing name alone (as the pin-count body-width difference shows) does not fully pin down the dimensions. And on NXP/Nexperia parts, the SOTxxxx internal code is a lookup key — resolve it to an outline drawing before you trust any dimension.
How to choose a SOT package
Work the constraints in this order:
- Is it a power part (LDO, medium-power transistor)? Go straight to a tabbed package — SOT-223 for over ~0.5 W, SOT-89 for moderate power in a smaller body. Plan the copper pour first, not last.
- Is board area the hard limit and power is low? Step down the shrink path: SC-70 (SOT-323) then SOT-523, accepting higher θJA and harder rework.
- How many pins? Three or four → SOT-23-3 or SOT-143; five or six → SOT-23-5/-6 or SC-88 (SOT-363). Remember the -5/-6 body is wider than the -3.
- Will it be hand-assembled or reworked? Prefer SOT-23 at 0.95 mm pitch; 0.5 mm-pitch SOT-523 is unforgiving with an iron.
- Do you need a second source? Anchor the requirement to the JEDEC outline (for example TO-261AA for SOT-223) so alternates from other vendors drop onto the same footprint.
- Are you only decoding an existing part? Resolve the name through the synonym and JEDEC map above, then confirm pinout and dimensions against that exact datasheet.
Design mistakes that cause returns
- Assuming a universal SOT-23 pinout. Assignments vary by device; a wrong footprint bricks the board. Check every datasheet.
- Treating SOT-23-3 and SOT-23-5 footprints as identical. The 1.6 mm-wide 5-lead body needs its own land pattern.
- Under-coppering a SOT-223. Without a pour under the tab, an LDO that “should” work overheats — the 1.36 W example above lands at 122 °C bare.
- Reading an NXP SOTxxxx code as a size. SOT1123 is a 324-ball BGA; the number is not a dimension.
- Ignoring seated height in low-profile designs. If height is the constraint, specify a TSOT-23 or an SC-70-class part rather than a standard SOT-23.
Frequently asked questions
What does SOT stand for?
SOT stands for Small Outline Transistor — a small, plastic, surface-mount package with gull-wing leads on two sides. It was introduced to replace through-hole transistors like the TO-92, and now houses diodes, references, and small regulators as well as transistors.
What is the difference between SOT-23 and SOT-223?
SOT-23 is a small signal package (2.9 × 1.3 mm, 0.95 mm pitch) with no heat-spreading feature, good for a few hundred milliwatts. SOT-223 is much larger (6.5 × 3.5 mm) with an exposed tab that couples to board copper, handling over a watt with a proper pour. Choose SOT-223 for power, SOT-23 for signal.
Is SOT-23 the same as SC-70?
No. SC-70 is the JEITA name for the SOT-323 family, which is smaller than SOT-23 — a 2.0 × 1.25 mm body at 0.65 mm pitch versus SOT-23’s 2.9 × 1.3 mm at 0.95 mm. SC-70 is a shrink of the SOT-23 concept, not the same package.
What is the SOT-89 package used for?
SOT-89 is a medium-power surface-mount package (JEDEC TO-243) with a die pad and enlarged center lead that spread heat into the board. It suits medium-power transistors and small LDO regulators that need more dissipation than a SOT-23 but less board area than a SOT-223.
Is SOT-23 the same as TO-236?
The 3-lead SOT-23 (SOT-23-3) is registered by JEDEC as TO-236AB (early parts as TO-236AA), so yes for that variant. The 5- and 6-lead SOT-23 parts are registered separately under JEDEC MO-178, not TO-236.
What is a TSOT package?
TSOT (Thin SOT) is a reduced-height version of an SOT package with the same footprint, used where vertical clearance matters — under shields or in card-form-factor designs. A TSOT-23 drops into a SOT-23 land pattern but sits lower.
The bottom line
Pick by the constraint that actually binds. Power part → tabbed SOT-223 (or SOT-89), and lay the copper before anything else. Tight board, low power → shrink down the SC-70 / SOT-523 path and accept the thermal and rework cost. More pins → SOT-23-5/-6 or SC-88, with a footprint sized for the wider body. Then verify pinout and dimensions against the exact datasheet, and anchor any second-source requirement to the JEDEC outline number. And if you meet a SOTxxxx code in the four digits — like SOT1123 — look it up before assuming anything; in that system the number is a registration key, not a size.
