The theoretical limit of a lateral wide band-gap semiconductor (WBS) power device was estimated for SiC, GaN and diamond. The lateral WBS device realizes ultra-low on-resistance due to a very short gate-drain offset, and a power integration circuit with very high power can be easily realized even with a small chip. The lateral WBS devices with breakdown voltage of over 1 kV realized on-resistance below 1 mOmegacm(2). For the breakdown voltage of over 10 kV, diamond devices are attractive due to the large critical field (5.6 MV/cm). Although the WBS device realizes drastic reduction of both the chip area and the power loss, the heat dissipation technique and high current density switching capability are also important for bringing out the potential of the WBS device. (C) 2004 Elsevier Ltd. All rights reserved.