Senate Select Committee on Ethics
The Senate Select Committee on Ethics is authorized to receive and investigate allegations of improper conduct which may reflect upon the Senate, violations of law, violations of the Senate Code of Official Conduct and violations of rules and regulations of the Senate; recommend disciplinary action; recommend additional Senate rules or regulations to insure proper standards of conduct; and report violations of law to the proper federal and state authorities. (source)
The chair is always selected from the majority party and the ranking member is the most senior member of the minority party.
The majority party ensures it has a majority on every committee.