A microelectromechanical system (MEMS) apparatus is described. The MEMS apparatus may comprise inertial sensors and energy harvesters configured to convert mechanical vibrational energy into electric energy. The harvested energy may be used to power an electronic circuit, such as the circuit used to sense acceleration from the inertial sensors. The inertial sensors and the energy harvesters may be disposed on the same substrate, and may share the same proof mass. The energy harvesters may include a piezoelectric material layers disposed on a flexible structure. When the flexible structures flexes in response to vibration, stress arises in the piezoelectric material layer, which leads to the generation of electricity. Examples of inertial sensors include accelerometers and gyroscopes.