The present invention relates generally to semiconductor devices and more particularly, to a structure and method of forming a partially depleted semiconductor-on-insulator (SOI) junction isolation structure using a nonuniform trench shape formed by reactive ion etching (RIE) and crystallographic wet etching. The nonuniform trench shape may reduce back channel leakage by providing an effective channel directly below a gate stack having a width that is less than a width of an effective back channel directly above the isolation layer.