You need to be commissioned as an officer and get a pilot slot.  To be commissioned, you will need to go through a service academy, ROTC at a civilian or private military college, or OTS after graduation. 

In the AF, about 40 percent of pilot slots go to the academy, 40 percent to AFROTC, and the remainder to OTS (so I am told).

The AF likes technical/science degrees, but it is NOT a requirement. 

resources:

wantscheck.org

academyadmissions.com

afrotc.com

(AF OTS website)