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Abstract Geometric diodes (GDs) represent a relatively unconventional class of diode that produces an asymmetric current response through carrier transport in an asymmetric geometry. Synthesized from the bottom up, Si nanowire‐based GDs are three‐dimensional, cylindrically symmetric nanoscale versions capable of room‐temperature rectification at GHz‐THz frequencies with near zero‐bias turn‐on voltages. Here, by fabricating three‐terminal n‐type Si nanowire GDs with axial contacts and an omega‐gate electrode, a distinct class of reconfigurable self‐switching geometric diodes (SSGDs) is reported. Single‐nanowire SSGD device measurements demonstrate a significant dependence of diode current and polarity on gate potential, where the diode polarity reverses at a gate potential of ≈−1 V under specific grounding conditions. Finite‐element modeling reproduces the experimental results and reveals that the gate potential—in combination with the morphology and dopant profile—produces an asymmetric potential along the nanowire axis that changes asymmetrically with axial bias, altering the effective conductive channel within the nanowire to yield diode behavior. The self‐switching effect is retained in two‐terminal SSGD devices, and modeling demonstrates that both three‐terminal and two‐terminal devices support rectification through THz frequencies. The results reveal a new mechanism of operation for nanowire‐based GDs and characterize a new type of self‐switching diode with reconfigurable polarity.