Various methods and circuital arrangements for complete turn OFF of branches of a multi-branch cascode amplifier are presented. According to one aspect, a protection circuit coupled to a source node of an output transistor of a branch couples a reference voltage to the source node of the output transistor when the branch is turned OFF, and decouples the reference voltage from the source node when the branch is turned ON. According to another aspect, the protection circuit includes a switch whose off capacitance is sufficiently low so as not to affect performance of the branch when the branch is ON, and whose on resistance is sufficiently low to sufficiently reduce an RF amplitude at the source node of the output transistor when the branch is OFF and other branches are ON, and therefore allow use of low-voltage thin-oxide transistors in the branch. Further aspects include a second switch and use of transistor switches.