The non-monotonic DIBL behavior observed with variation in back gate voltage, in thick front gate oxide (FGOX) long channel FDSOI transistor is presented in this work. The physical origin of this behavior is the fringing field induced channel potential variation, from drain to drain side channel region, through thick FGOX for negative back bias, and through BOX for positive back bias. Additonally, we study the impact of channel length scaling on non-monotonic DIBL with variation in back gate voltage. © 2019 IEEE.