||Wearable devices have been rapidly expanding their use in everyday life, enabling on-spot access to abundant information that was not available before. Despite the notable increase, wearable devices face one fundamental challenge: a limited operation lifetime. Traditionally, wearable devices operate by consuming energy that is stored in a battery. While they could increase their operation lifetime by increasing the battery size, it would only increase the size of the whole wearable system. Harvesting energy from ambient has been suggested as one of the most promising methods to overcome such a challenge because it can perpetually work and does not have limitations in a lifetime. As readily-available ambient sources, human activities have been heavily investigated because of their on-spot availability to wearable devices, and walking, in particular, is considered holding the highest power amounts up to 324 W. However, harvesting energy from walking still remains challenging because it suffers an easy break or deformation of delicate microstructures under a large pressure, less displacement due to tiny scales or discomfort due to bulky and rigid components. To address such issues and realize practical energy harvesting from walking, a concept of a hydraulic electromagnetic energy harvester (HEEH) can be utilized. The proof-of-concept device, HEEH, utilized free movements of incompressible fluids through multiple channels to hydraulically de-amplify a body weight into a small force, to change the force direction within a low-profile form and to provide comforts in a iv wearable device. This dissertation discusses the details in design, fabrication, technology developments and test results of the novel proof-of-concept HEEH. The HEEH with 5- channels & 7-layers produced an average power of 784.04 mW at 3 Hz from a testing setup, which mimicked fast running (3.2 Hz) condition and 625 mW from normal standard walking of 2 Hz. The HEEH was also integrated with two types of heaters to produce temperature rises of 2.0 & 3.2oC and the heating rates of 12.0 & 1.6oC/min, respectively, from polysilicon (0.15×0.1mm2, 6.05e-6s of thermal time constant) and copper heaters (78×28mm2, 8.31s of thermal time constant). Such heating performance of the HEEH is the 1st results of its kind.