The Senate has a membership of 40 Senators elected for 4-year terms, 20 to begin every 2 years.

During his or her lifetime a person may serve no more than 12 years in the Senate, Assembly, or both, in any combination of terms.

Since the passage of Prop 28 in 2012, legislators first elected on or after November 6, 2012, are limited to a maximum of 12 years.

Prop 140, passed in 1990, affects any members elected prior to November 6, 2012, and limits them to a maximum of two four-year terms (eight years total). Voters in the 20 odd-numbered districts of the California State Senate will elect their representatives. There are 16 Democratic-held senate seats up for election in 2024, 3 Republican-held seats, and 1 open seat with no incumbent.
Here is a review of the first set of California state senate candidates.