46 Pa. Stat. § 42.146
All vacancies that may occur or exist by death, resignation or otherwise, of any of the officers or employes provided for by this act during any regular, special or extraordinary session of the Legislature shall be filled by election or appointment as provided for in this act. If any vacancy shall occur during the recess of the Legislature in the Office of President pro tempore of the Senate or of the Speaker of the House of Representatives, the duties of said office shall be performed by the Majority Leader of the Senate or of the House of Representatives, as the case may be.
All other vacancies that may occur during the recess among the elective officers or employes of the Senate or of the House of Representatives shall be filled by appointment by the President pro tempore of the Senate or by the Speaker of the House of Representatives until the next regular, special or extraordinary session of the Legislature. Vacancies occurring at any time among appointive officers and employes shall be filled by the respective officers authorized to appoint said officers or employes.
46 P.S. § 42.146