specify source and gate of FETS

Hi,How can i specify GATE and SOURSE and DRAIN of a mosfet without using datasheet?is there any way?please help me.

You can use the diode check function of a multimeter to find the body diode of the mosfet. That will tell you the drain and source. The correlation of cathode/anode to drain/source will, of course, depend on whether it is a P or an N channel mosfet.

As Chris noted, you can find the body diode direction to determine the drain and source. For an N-MOSFET the anode is the source terminal. For a P-MOSFET the anode is the drain.

ChrisP58 said:

You can use the diode check function of a multimeter to find the body diode of the mosfet. That will tell you the drain and source. The correlation of cathode/anode to drain/source will, of course, depend on whether it is a P or an N channel mosfet.

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And the gate will look "open" with respect to either the source or drain. I try to find the source-drain pins first, and that leaves the gate...

With a three-lead device, there are six different Ohmmeter measurements you can do. Only one of the six will normally show a forward biased diode. However, if the gate is left with a static charge that turns on the FET, the source-drain pin pair can show a "short" in either direction, which should disappear if the gate pin is momentarily shorted to what you think is the source pin.