A self-regulating current source is formed by a PMOS current mirror and an interconnected pair of NMOS transistors. The NMOS transistors are sized differently and forced to operate at similar currents. The difference of the Vgs voltages of the NMOS transistors is impressed across the resistor to develop a stable output current. In particular, the current source starts reliably at low supply voltages and operates to reliably generate a stable low output current at a well-controlled operating point. The self-regulating current source can be used effectively as the watchdog current source of a power-on reset circuit to ensure reliable and robust operation even at low Vdd voltage values.