The Marvel Universe Wiki reads: Peter Parker graduated high school and earned a science scholarship to Empire State University (ESU) for achieving the highest scholastic average in Midtown High's history.
So while it doesn't say what the major was, it would have had to at least be science based.
ADDON:
At some point (in Amazing Spider-Man) adult Peter Parker decides to leave the Bugle and teach high school science.
There's a strong hint there.
scifi.stackexchange.com/users/224/MPelletier
There is at least some very strong indirect evidence.
To make his web shooters he needs some deep knowledge of chemistry.
Additionally, I think at the earliest in The Amazing Spider-Man 6 his teacher Curt Connors is introduced.
And it is stated clearly that he is a Professor of biochemistry .
Another piece of indirect evidence that Peter Parker's major is chemistry or biochemistry.
Later versions of the character differ from this.
But the Peter Parker of the original (Lee / Ditko) run studied chemistry.
scifi.stackexchange.com/users/60920/drmanhattan
(Click links to see the comic pages this information is sourced from.)
In Amazing Spider-Man #28, Peter graduated from Midtown High School with a science scholarship to Empire State University.
In various 1960s issues such as Amazing Spider-Man #31 , #45 and #47 , it was stated or otherwise indicated that Peter was a science major at ESU.
According to a caption in Marvel Team-Up #27 , Peter was specifically a physics major during his undergraduate studies, and a caption in Marvel Team-Up #28 said he was pursuing a bachelor's degree in physics.
In Amazing Spider-Man #243, he received a letter from Empire State University informing him that he'd been approved for second-year studies in the graduate program of the department of bio-physics, although he dropped out due to money troubles.
Peter demonstrated computer hacking skills in Civil War: Front Line #9.
He also developed Webware , a mobile Internet device with nanotech-based, self-reconfiguring software and hardware , while running Parker Industries in Amazing Spider-Man Vol.
4.
And he's dabbled in electronics since his earliest appearances, in issues such as Amazing Spider-Man #2 and #11 .
He wasn't shown using computers much during his college days, but computers weren't anything like as ubiquitous when those stories were published as they are now.
scifi.stackexchange.com/users/122024/LogicDictates
According to the Game Spider-man.
Shattered Dimension.
He finished BS Physics.
In the amazing universe though.
Earth 616.
scifi.stackexchange.com/users/15714/Ely
According to the Official Handbook of the Marvel Universe (Vol. 1 #10) Peter's major in college was Biophysics .
Latterly, the Official Handbook of the Marvel Universe (Vol. 4 #2) indicates that his Doctoral studies are in Biochemistry
scifi.stackexchange.com/users/20774/Valorum
From everywhere I've seen, It doesn't mention what his major is.
I would assume it was photo journalism based on his career with the Bugle, but he also showed an aptitude for biomechanics, engineering and biology.
He might have double majored.
scifi.stackexchange.com/users/1109/OghmaOsiris
SCIENCE!
Seriously, though, depending on which iteration of Spidey you pick, I would think something like mechanical engineering or (later) biochemistry.
scifi.stackexchange.com/users/1150/Chris B. Behrens
I think his major was science because in the amazing Spider-Man, Peter Parker was the 2nd in class in Science, the 1st one was Gwen Stacy.
And when he came to oscorp, dr curt Connors was delighted by his science knowledge.
But creating the web shooters has something with engineering
scifi.stackexchange.com/users/73785/Daniel
In which area did Peter Parker major in at university?  Did he ever show any computer hacking skills or other computer-related interests (computer science)?
What was Peter Parker’s college major?
scifi.stackexchange.com
<spider-man><marvel><the-amazing-spider-man>
scifi.stackexchange.com/questions/27163
scifi.stackexchange.com/users/7902/delta_omega
Peter Parker was a science student. In Amazing Spider-Man #28, Peter  graduated from Midtown High School  with a science scholarship to Empire State University, where he was the 2nd in his class in Science. In Amazing Spider-Man #243, he received  a letter from Empire State University  informing him that he'd been approved for second-year studies in the graduate program of the department of bio-physics. His major is science; specifically biophysics.
His major is science; specifically biophysics.