This paper introduces the monolithic association of five sensors in an Inertial Measurement Unit (IMU). Two thermal accelerometers, two piezoresistive magnetometers, and one seismic accelerometer have been co-integrated using two different industrial processes thus demonstrating the versatility of the proposed solution. The first prototype is a System in Package (SiP) with signal processing on a separate die, while the second prototype is a full-CMOS System on Chip (SoC). The proposed architecture is detailed including the front-end electronics which is optimized to address noise and power consumption issues. Based on characterization results, good resolutions are obtained for each sensing axis. Using these results, the IMU is evaluated in the context of an Attitude and Heading Reference System (AHRS). Results demonstrate the suitability of the proposed five axis architecture, for full 3D orientation determination, with acceptable resolutions.