Abstract: Miniaturization is a trend of development toward practical applications for diamond nitrogen-vacancy centers-based sensors. We demonstrate a compact diamond magnetic field sensor device using a standard microfabrication process. A single-crystal-diamond plate is embedded in a cavity formed with stacking of three silicon chips. Thermal compression bonding is implemented at silicon–silicon and diamond–silicon interfaces ensuring mechanical robustness. The specific construction volume for the essential sensor component is about 10 × 10 × 1.5 mm³. By integrating a gradient index lens pigtailed fiber to the sensor device, 532-nm laser light and emitted fluorescence share a common path for excitation and detection. An omega-shaped transmission line for applied microwave power is fabricated directly on the surface of diamond. The integrated sensor device exhibits an optimized sensitivity of 2.03 nT·Hz^−1/2 and over twofold enhancement of fluorescence collection efficiency compared to bare diamond. Such a sensor is utilized to measure a magnetic field change caused by switching a household electrical appliance.