Transistors, methods of manufacturing thereof, and image sensor circuits with reduced random telegraph signal (RTS) noise are disclosed. In one embodiment, a transistor includes a channel disposed between two isolation regions in a workpiece. The channel has edge regions proximate the isolation regions and a central region between the edge regions. The transistor includes a gate dielectric disposed over the channel, and a gate disposed over the gate dielectric. The transistor includes a voltage threshold modification feature proximate the edge regions configured to increase a voltage threshold of the transistor proximate edge regions relative to the central region of the channel.