Does this MOSFET datasheet contain missing data?
It might help if you looked at the safe operating area for the MOSFET in question: -



The X axis is voltage and you can see it is limited to 100 volts. The Y axis is current and this is limited to 140 amps i.e. the "Pulsed Drain Current" specified in the "Absolute Maximum Ratings" table on page 1.

What this tells you is that if you could turn on and off the MOSFET in 10 us you could take 140 amps but with a limited voltage of about 60 volts. That's an instantaneous power of 8.4 kW.

Alternatively you could withstand 100 volts but at a reduced current of about 90 amps. That's an instantaneous power of 9 kW.

This is very much defined as a "single pulse" (bottom left corner of graph) i.e. it is a single event of 10 us.

If your pulse was 10 ms then you could withstand 100 volts whilst taking no more than about 2.5 amps. Notice now that the power taken during this much longer pulse is only 250 watts.

Eventually (if the graph showed this detail) you would find that the continuous power rating of 160 watts means a continuous current of 1.6 amps whilst withstanding 100 volts. Or it could mean 10 amps at 16 volts or 16 amps at 10 volts etc..


  What I mean by "OFF" is when the gate voltage is zero (no gate signal)
  or when the MOSFET is reverse-biased (i.e. Drain voltage is 0V and
  source voltage is +100V).


You can't apply anything more than about a volt in reverse. The body diode in the MOSFET will conduct and, if the reverse supply could provide more than 42 amps, the body diode would break and so would the MOSFET. See "Source-Drain Ratings and Characteristics" for numbers on page 2.

See also this on the last page: -