In this paper, we present our recent progress of a high sensitivity complementary metal-oxide semiconductor-microelectromechanical systems (CMOS-MEMS) inertia sensor and its application to early-stage diagnosis of Parkinson’s disease. The feature of the CMOS-MEMS sensor is the use of gold proof mass. High density of gold enables us to increase sensitivity by reducing thermo-mechanical noise that is inversely proportional to proof mass. We then show the developed CMOS-MEMS multi-physics design environment. An equivalent circuit of a MEMS accelerometer has been designed to simultaneously understand both the mechanical and the electrical behaviors. One of the potential applications of the high sensitivity inertia sensor is also discussed by focusing on early-stage diagnosis of Parkinson’s disease.