Transient voltage suppressors for electronic circuits. with power supply voltage of 3.3 V or lower are urgently needed but unavailable due to excessive leakage of low-voltage reversed p–n diodes. We analyzed several candidate device structures by using two-dimensional device simulation. Adopting the punchthrough mechanism in an n+p+p-n+structure rather than the traditional avalanche mechanism in a p+n+structure, we can achieve low standoff voltage with excellent performances in low leakage current, low capacitance, and low clamping voltage. The new device appears to be satisfactory for protecting future electronic systems with power supply voltage at least down to 1.5 V.