Do UC's ONLY look at 10-12 grades?

I was wondering because I got a 2.83 1st semester of freshman year, 3.44 2nd semester…but then I really improved and got straight A’s throughout the rest of hs.

You’ll need to report them and they will see and consider them to some extent, but in your case your freshman year will only help. They love that sort of upward trend.

Freshman year is not considered in GPA but it’s not totally ignored because class rank is considered.

UCs do not consider class rank as determined by the high school. However, things which have some correlation to class rank are considered. An example is ELC determination, where your UC-calculated GPA is compared with the historic top 9% UC-calculated GPA of your high school.

While grades in 9th grade courses do not count toward the UC-calculated GPA, they grades are visible to admissions readers, and any D or F grades disqualify those courses from counting toward a-g subject requirements (although foreign language and some math courses may be validated by higher level courses).

^ Thanks for the clarification.