Here's a breakdown of spectral classes and their temperature ranges:

* O: 30,000 - 50,000 K (blue)

* B: 10,000 - 30,000 K (blue-white)

* A: 7,500 - 10,000 K (white)

* F: 6,000 - 7,500 K (yellow-white)

* G: 5,200 - 6,000 K (yellow)

* K: 3,500 - 5,200 K (orange)

* M: 2,000 - 3,500 K (red)

As you can see, O-type stars have the highest temperature range, making them the hottest.