TO264 package at 100 Amps
Datasheet link &amp; device name please. !!!!
You will often see the notation"package limited" for very high energy devices.   

Perhaps a IXFK-FX98N50P3 Rdson &lt;= 50 mOhm - wow. 500W dissipation at 100A :-)

About  0.2 C/W Rth_cs
So 100 C junction rise above heatsink.

I pulse max is 245 A T junction limited. 
This is "really" a 49A part and still rather unhappy at that level.
About 2.25V Vds at 25C at 50A and about 5V at 125C Tj (figs 1-3)

So still 250W at 50A once it gets hot.  

The only reason you'd use a device with this apparently abysmal spec is its 500 V Vds rating.

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For about double the price ($US27/1)
STY139N65M5
17 milliOhm at 25C. About 2x that at 125 C.
Still an inadequate package.
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For $US59/1 you get an Isotop pkg that starts to work.
650V 143A. 
Rdson is 12 mO typical at 25C and a bit under double that at 125C.
Tjc is about as above but the package can tolerate heat and current.
melting the screws would be a challenge - not an unmeetable one :-).  

STE145N65M5