That is an IRFZ46N. You will need to replace ALL IRFZ46Ns (search octopart.com for IRFZ46NPBF) there are 16 in that amp. Before putting in new parts, with the IRFZ46Ns removed, you should power the amp on and check for ~5v DC at all the gate resistors.
The cause of the blown 46Ns is most likely a shorted IRFB31N20D in the output. Look for anything close to 0 ohms between all three legs on the IRFB31N20Ds (Q130-Q139, legs 1 to 2, 1 to 3, 2 to 3). If you do find anything near 0 ohms you should replace all outputs in that bank (there are 2 banks of 5).
After that you may find that one of the output inductors has a shorted turn (extremely common in these clone amps).