The present disclosure provides a semiconductor structure having a vertical fin with an oxidized sidewall and a method for preparing the semiconductor structure. The semiconductor structure includes a substrate, a top source/drain, a channel fin, a gate structure, a top cathode/anode, and a vertical fin. The substrate has a bottom source/drain and a bottom cathode/anode. The top source/drain is disposed above the bottom source/drain of the substrate, and the channel fin connects the top source/drain to the bottom source/drain of the substrate. The gate structure is disposed on the channel fin. The top cathode/anode is disposed above the bottom cathode/anode of the substrate, and the vertical fin connects the top cathode/anode to the bottom cathode/anode of the substrate, wherein the vertical fin has an oxidized sidewall.