Calculate junction temperature of MOSFET during pulse

I want to find out how hot the junction gets during a 300 us pulse of 400 A peak current.

Datasheet of MOSFET, Datasheet

From the datasheet I came across this graph,

For a pulse of 300 us or 3*10^-4 seconds, I found Zth = 0.04 K/W

So, if I = 400 A and Rdson = 0.07 ohms (From datasheet), then

P = I^2*R = 400^2 * 0.07 = 11200 W

Then, Zth = 0.04*11200 = 448 K = 175 degrees Celsius

Therefore Junction Temperature = 175 + Ambient(Assuming 30) = 175+30 = 205 C

Is that correct ?

Answer

Your math looks reasonable.. however that device will not withstand anywhere near 400A. Especially not for 300uS.

Looking at the safe operating curve... The maximum you can do for 300uS is about 100A if your Vds is less than 20V.

So basically the temperature thing is mute. You will let out the smoke.