Two-transistor devices protect electrical circuits from sustained overcurrent conditions. Some cases provide normally-on depletion mode transistors biased into enhancement mode for lower impedance during normal current conditions, and then the transistors are biased into blocking depletion mode during sustained overcurrent conditions to block the current to the circuit. Optionally, the devices have only two terminals and require no auxiliary power to operate. Other cases provide protective circuitry for the transistors' gates, timing circuitry designed to ignore brief nuisance spikes, and/or timing circuitry to delay resetting the device until the current has returned to an acceptable level.