The 2020 Colorado Senate elections took place on November 3, 2020, with the primary elections held on June 30, 2020. Voters in 18 out of 35 districts of the state senate elected their representative for a four-year term. It coincided with the state House elections and the biennial United States elections. The Democratic Party retained control of the Senate, winning 20 seats, and increased their majority by one, gaining the 27th district from the Republican Party.
In the previous state Senate election (2018), the Democrats claimed control of the chamber from the Republicans, gaining two Republican seats and one independent (formerly Democratic senator) seat. That resulted in a 19-seat Democratic majority. Therefore, for Democrats to have lost their absolute majority in the Senate in this election, Republicans and other parties would have needed to gain at least two more seats.
One Democratic and three Republican incumbents were term-limited and prohibited from seeking a consecutive third term.
Bold - Gain<br /> Italics - Hold, new member
Seats where the margin of victory was under 10%: