I'm aware of how fraught with speculation questions about the Sea Peoples are. That said, I'm under the impression there's a good deal of circumstantial evidence that suggests the Philistines were decendents of displaced Greeks.
I answered a similar question earlier today, coincidentally. The tl;dr is that there's some evidence, mostly in the artifacts they left behind, but also evidence from their language (that's Indo-European, not Semitic).