16 Pa. Stat. § 7721
In every county of this Commonwealth having over one million five hundred thousand inhabitants, the district attorney shall have the power to appoint one or more assistants, learned in the law, not exceeding thirty in number, to assist him in the discharge of his duties. One of said assistant district attorneys shall receive a salary of seven thousand five hundred dollars per annum; one of said assistant district attorneys shall receive a salary of six thousand five hundred dollars per annum; three of said assistant district attorneys shall receive salaries of six thousand dollars per annum each; eight of said assistant district attorneys shall receive salaries of five thousand dollars per annum each; four of said assistant district attorneys shall receive salaries of four thousand dollars per annum each; and thirteen of said assistant district attorneys shall receive salaries of three thousand dollars per annum each. In the event of the appointment of a less number of assistants than thirty, the district attorney shall have the power to determine in which class, as to salaries, the appointee or appointees shall be placed. Said salaries shall be paid out of the county treasury.
16 P.S. § 7721