iMac Graphics Processor heat sink.

[MacOCD]

So mines at 142 degrees... that seems high to me but i am not really sure... i guess it is a heatsink it should be trapping heat i guess.

 

[AlexisV]

The GPU will be 142degrees. Unless you've opened your Mac and tested along the heatsink piping, you won't know the temperature of that.

142 is fine. It's a chip. It gets hot.