Semicolons and commas can be used together to show groupings within a sentence.
Use semicolons with items in a series when the items in the series contain internal commas.
Without the semicolons, the reader must sort out the major groupings, distinguishing between important and less important pauses according to the logic of the sentence. By inserting semicolons at the major breaks, the writer does this work for the reader.
Exercise: The semicolon and the comma 1
Exercise: The semicolon and the comma 2
Exercise: The colon, the semicolon, and the comma
Related topics:
Semicolons between independent clauses
Comma with items in a series