This thesis presents new designs of three dimensional magnetic field sensors in BiCMOS technology. The detailed design of the merged structure device by common diffusion and the high gain transduction circuit are presented. The merged structure has the advantage of less area, less external contacts and less parasitic capacitance. Cross-sensitivity is also eliminated by employing the merged structure. Three active on-chip loads are introduced to improve the sensitivity. The SPICE simulation results show that when a relative change in current ΔI/I is 0.001, about 13.6 mV and 8.5mV can be detected at the output in X(or Y) and Z directions, respectively. The experimental results from a standard (non-merged) BiCMOS magnetic sensor is presented. The 3-D sensor element has been integrated with the signal processing circuits to build a monolithic 8 x 8 sensor array. The detailed SPICE simulation results on the critical path shows the array can be operated with elimination of column-to-column offset voltages under a maximum scanning clock speed of about 0.5MHz. The array structure can find application in precise manufacturing as a position sensor.