This is some of what the Bible has to say. As far as whether or not they are Semitic, there seems to be two different views.
The International Standard Bible Encyclopedia presents the case that they are and Aston's Bible Dictionary presents the case they are not.
It is too much to post here especially the ISBE reference.
Hope this helps.
Gen 10:6 And the sons of Ham; Cush, and Mizraim, and Phut, and Canaan.
Gen 10:13 And Mizraim begat Ludim, and Anamim, and Lehabim, and Naphtuhim,
Gen 10:14 And Pathrusim, and Casluhim, (out of whom came Philistim,) and Caphtorim.
1Ch 1:11 And Mizraim begat Ludim, and Anamim, and Lehabim, and Naphtuhim,
1Ch 1:12 And Pathrusim, and Casluhim, (of whom came the Philistines,) and Caphthorim.
Aston's = Easton's Bible Dictionary.
Genesis seems to indicate that the Phillistines were Hamitic, related to Egyptians and other Africans - definitely not Semites.
It seems neither modern scholarship nor the Bible identifies them as racial Semites, although intermarriage and the adoption of others' cultural norms cloud these kinds of isssues.