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This paper reports a new micromachined fluxgate sensor with extremely low power consumption using a localized core saturation method. The extremely low power consumption has been achieved by shrinking the magnetic core width wound by the sensing coils, 10 times smaller than that wound by the excitation coils. With such core configuration, the magnetic field within sensing coils will be enhanced several times larger than that within excitation coils. This will thus allow the fluxgate sensor to be operated in a localized core saturation mode. That is, only relatively small amount of excitation current is needed to saturate the sensing core and induce the fluxgate effect at the sensing coils while the excitation core is not saturated yet. The device exhibits a power consumption of ~4 mW, sensitivity of 600 V/T at 60 muT, and sensor span of ~250 muT In comparison with our previously reported micro-fluxgate sensor the newly developed sensor consumes 25 times less power but at the expense of sensor span and linearity.