This invention provides a semiconductor device, which is used to manufacture two lateral high-voltage devices on the same substrate, where the voltages between maximum voltage terminals and minimum voltage terminals of the two devices have not too much difference. Both devices are formed on two different surface regions with a small isolation region in-between the two regions. When the semiconductor region(s) of the isolation region is fully depleted, its effective electric flux density emitted to the substrate is of a value between the values of its adjacent regions of said two semiconductor devices. The figure presented here schematically shows the structure used to form a low-side high-voltage n-MOST and high-voltage n-MOST and M1, where their terminal voltages are very close.