A switch regulator includes an inductor, a reference transistor, a first switching transistor, and a second switching transistor. The first switching transistor includes a gate electrode, a first main electrode (e.g., a source or a drain), and a second main electrode (e.g., a source or a drain). The first switching transistor is coupled in series with the inductor when it is turned on by a clock. The first main electrode (e.g., the source or the drain) of the switching transistor is connected to a ground or a fixed voltage power supply. A reference voltage may then be generated by flowing a current through the reference transistor. As such, the switch regulator contains an over-current detector that is flexible in size of current to be detected while consuming a relatively small amount of space and having substantially low cost on the overall efficiency of the switch regulator.