16 Pa. C.S. § 14304
If a vacancy occurs in the office of district attorney in a county of the second A, third, fourth, fifth, sixth, seventh or eighth class, the judges of the court of common pleas shall, upon a showing that the first assistant district attorney satisfies the requirements of section 14301 (relating to district attorney, qualifications, eligibility and compensation), appoint the first assistant district attorney to fill the office of district attorney and discharge the duties of the district attorney until the first Monday in January following the next municipal election occurring not less than 90 days after the occurrence of the vacancy. If the first assistant district attorney is unwilling or unable to serve or does not satisfy the requirements of section 14301, the judges of the court of common pleas shall fill the vacancy by the appointment of a competent individual who satisfies the requirements of section 14301 to fill the office until the first Monday in January following the next municipal election occurring not less than 90 days after the occurrence of the vacancy.
16 Pa.C.S. § 14304