A micromachined magnetic field sensor integrated with electronics is disclosed. The magnetic field sensors utilize Hall-effect sensing mechanisms to achieve 3-axis sensing. A Z axis sensor can be fabricated either on a device layer or on a conventional IC substrate with the design of conventional horizontal Hall plates. An X and Y axis sensor are constructed on the device layer. In some embodiments, a magnetic flux concentrator is applied to enhance the performance of the magnetic field sensor. In some embodiments, the magnetic field sensors are placed on slope sidewalls to achieve 3-axis magnetic sensing system. In some embodiments, a stress isolation structure is incorporated to lower the sensor offset. The conventional IC substrate and device layer are connected electrically to form a 3-axis magnetic sensing system. The magnetic field sensor can also be integrated with motion sensors that are constructed in the similar technology.