Legal Question in Employment Law in California

It's entirely up to the company policy and rules, not the 'law'.

Just to clarify Mr. Nelson's answer, the company is required by law to honor the company's bonus payment policy that was in place at the time the bonus was earned. Furthermore, if the bonus was actually earned as part of a compensation plan, as opposed to a discretionary bonus, it was vested when earned. There are many other types of bonuses, however, including discretionary bonuses and retention bonuses that can legally be cancelled if the employment terminates before payment is due. So the nature of the bonus and the policy or plan under which it is granted will determine whether or not the law requires that it be paid after employment ends.