Amendments to the Constitution, approved by a joint session of Congress on August 16, 2005, eliminated non-directly elected senators from March 11, 2006, the day 20 newly elected senators were sworn in, leaving the total number of senators at 38, all directly elected. Previously, according to the Constitution of 1980, "designated" or "institutional" senators were appointed to the chamber. Two former heads of state, Eduardo Frei Ruiz-Tagle and Augusto Pinochet, were installed as senators for life. Pinochet later resigned from this position and Frei lost his seat in the 2005 reform. However, Frei remained in the Senate by winning an elective seat.

Created by Article 7 of the Provisional Constitutional Manual of 1812. It was composed of seven titular members (one for each province) and three alternate members and was supposed to serve as a counterbalance to the executive power of the Government Junta. The senators were directly nominated by the provinces in agreement with the central government. It functioned from November, 1812 to January, 1814, when it was reorganized to better respond to the problems caused by the successive military defeats at the hands of the advancing Spanish Army.

Created by Article 13 of the Provisional Government Manual of 1814. As its predecessor, it was composed of seven titular members (only) nominated by the provinces in lists of three from which they were selected by the Supreme Director. It functioned from March to July, 1814, when the Spanish Army captured Santiago, putting an end to the Patria Vieja government.

Created by Title III of the Constitution of 1818. It was composed of five titular members and five alternate members selected directly by the Supreme Director. It was supposed to function only when the lower house was not in function or could not meet, and had the power to enact "provisory rules" that had the same effect as laws (hence the "conservative" moniker, because it "conserved" the power.) It functioned from October, 1818 to May, 1822.