A novel concept of REBULF (REduced BULk Field) is proposed for the developing smart power integrated circuit with the thin epitaxy layer. The REBULF LDMOS structure is designed with N+ buried layer embedded in the high-resistance substrate. The mechanism of breakdown of the new device is that the high electric field around the drain is reduced by N+ buried layer, which causes the redistribution of the bulk electric field in the drift region of the REBULF LDMOS so that the substrate supports more biases. The critical condition of the REBULF technology is analyzed and validated by 2-D MEDICI simulation results, which is the product of the location of N+ buried layer and substrate's doping is not more than 1 x 1012 cm(-2). The breakdown voltage of REBULF LDMOS is increased by 75% in comparison to the conventional RESURF LDMOS from the simulation results. The experimental results show the high electric field around the drain is reduced as the depletion region spreads to N+ buried layer. Although the leakage has increased a little, this increase is not enough to cause the avalanche breakdown. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.