The present invention provides an ESD protection device with isolated islands and an n well. At least one of the isolated islands has an end apart from the boundary of a drain diffusion region of the ESD protection device, to form a gap between. The n well overlaps with the isolated islands and is kept at least a designated distance away from a channel region of the ESD protection device. An interlocked structure of isolated islands is also provided in this invention to direct ESD current flowing forward and backward to the channel region of the ESD protection device, thereby increasing the distributed resistance of the drain diffusion region. Several benefits, such as lower drain capacitance, lower standby power consumption and a wider range of adjustable resistance, are achieved.