A thin film lateral SOI power device comprises a substrate and a buried oxide layer (4) on the substrate; a silicon layer (6) on the buried oxide layer, the silicon layer having a laterally extending drift region; a dielectric layer on the silicon layer (6), the dielectric layer having a gate dielectric layer (18), a field dielectric layer (20) and a drift dielectric layer (22) having thickness larger than the thickness of the field dielectric layer (24) and a dielectric layer transition region (24) between the field dielectric layer and the drift dielectric layer; a gate (26) located above a channel region (27) in the first silicon layer thickness region (10) and extending as a field plate (28, 36,44) from the channel region (27) across at least the field dielectric layer (20); a drain (30) laterally spaced to the third thickness region (12) of the silicon layer (6); and a source (32) laterally separated from the gate; wherein in a drift region extending in the silicon layer (6) from the channel region (27) towards the drain (30), the doping dose (impurities per unit of area) is scaled such that a steady increase in concentration (impurities per unit of volume) produces a constant longitudinal electric field irrespective of thickness transitions in the silicon layer (6) and/or the dielectric layer (18,20,22) and/or the field plate (28). The method of fabricating the above thin film lateral SOI power device comprises scaling the doping dose in the drift region of the silicon layer such that a steady increase of the longitudinal doping density results in a constant electric field in the drift region of the silicon layer irrespective to thickness transitions in the silicon layer and/or the top oxide layer and/or the field plate. The driving in of the dopant in the drift region of the silicon layer is carried out after forming the top oxide layer.
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