There is hereby created within the state department of revenue a commission to be known and designated as the “State Tax Commission”. The director of revenue shall have no supervision, authority or control over such actions or decisions of the state tax commission as relates to its duties prescribed by law. The state tax commission shall be composed of three members, chosen from the two major political parties, who shall be appointed by the governor, with the advice and consent of the senate, one of whom shall be designated chairman, and to hold office for staggered terms of six years; provided, however, that of members first appointed, one member shall be appointed for a term of two years, one member for a term of four years, and one member for a term of six years. Each commissioner shall hold office until his successor shall qualify.