A novel system-on-chip (SOC) biomagnetic wearable sensor is presented in this paper. Wearable magnetic sensors have been developed for detecting tilt or geographic orientation. However, none of them can be applied for detecting the magnetic fields of the human body. To produce a low-cost, highly-reliable, wearable biomagnetic sensor, a CMOS Hall effect sensor with synchronous excitation sensitivity calibration is presented to reduce the inherent non-ideal drift of a Hall probe. Synchronous excitation utilizes an on-chip coil to generate a DC reference magnetic voltage at the output of the Hall probe by modulating the frequency of the coil to the frequency of the Hall spin current bias. With the proposed calibration method, the experimental results showed a sensitivity drift of 73 ppm per degree Celsius and required approximately 66 percent of the silicon area required by previous works. This work may open the gate to wearable biomagnetic sensors.