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I watched a youtube video explaining that the dot indicates the start of the source pin segment, and the 4th pin on the same side, is the gate. With a DMM, I get continuity between the dot pin and some other components only, but not the remaining 3 pins, which indicates to me that the dot indicates gate.

enter image description here

Is there a standard for dot for pinout, or can the dot indicate both source and gate depending on the MOSFET?

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    \$\begingroup\$ For me, the dot is pin 1 and for the other things look into the datasheet \$\endgroup\$
    – Mike
    Commented Sep 23, 2022 at 8:59
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    \$\begingroup\$ Did you look at the data sheet for the device? It will clearly show the connections. \$\endgroup\$ Commented Sep 23, 2022 at 10:37
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    \$\begingroup\$ You mention other components. Is this on a PCB? You can determine which pin is the gate, even if you don't have a part number, by looking at that. \$\endgroup\$
    – Hearth
    Commented Sep 23, 2022 at 12:28
  • \$\begingroup\$ Go to Digikey, use the search tools to find a MOSFET in the same package, you might get lucky. The first one I found: S: 1-3; G: 4; D: 5-8. Hook it up to a 5V circuit to test the theory. \$\endgroup\$
    – Mattman944
    Commented Sep 23, 2022 at 13:19
  • \$\begingroup\$ The standard for dot for pinout is the datasheet. \$\endgroup\$ Commented Sep 23, 2022 at 14:09

2 Answers 2

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The dot on such a package indicates pin 1 (as does the large chamferred edge). The pins are then in most cases numbered incrementally counting anti-clockwise from the dot:

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1 -|o |- 8
2 -|  |- 7
3 -|  |- 6
4 -|__|- 5

There is then no guarantee of any standard pinout for the device itself (the mapping from pin number to pin function e.g. gate, drain, etc.). It frequently happens that different manufacturers use the same pinout for things like MOSFETs and diodes, however different pinouts also frequently happen.

The easiest way to find out is to refer to the datasheet as this will tell you how pin numbers are related to their functions within a specific device.

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None of the above, both, and something else.

The pinouts are not standardized. Each manufacturer may choose their own way of connecting the pins - and may choose different connections for different models.

The only way to know for sure is to find the datasheet of the MOSFET and see how the manufacturer says to connect it.

What the dot tells you is where pin 1 is. You have to read the datasheet to find out what pin does what.

If the MOSFET isn't marked, then you'll have to try to find out from the circuit schematic what type of MOSFET it is. If the schematic and parts list don't say, then you'll have to analyze the circuit it is in to find out what each pin does.


The Youtube video may have been discussing a particular MOSFET, in which case the description might have been accurate. You can't take that description and apply it to all other MOSFETs, though.

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  • \$\begingroup\$ @slackexchange Do not use or buy components for which you cannot locate a datasheet. If there are no markings and you have no datasheet, how do you even know it's a MOSFET to begin? How do you know the pinouts? How do you know the maximum voltage and current it can tolerate? How do you know what voltage is needed to drive it? You don't know anything about it. \$\endgroup\$
    – DKNguyen
    Commented Sep 23, 2022 at 14:28
  • \$\begingroup\$ Thanks, + also, to the other answers.. \$\endgroup\$ Commented Sep 24, 2022 at 6:20

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