Abstract: Background: Energy harvesting is the process that uses ambient energy from the environment to produce electricity and thus replacing existing sources of power supply especially the battery. Due to increasing demand of energy harvester in the low power electronic applications, the researchers have been encouraged to review and study about this system. Most of them are focusing on improving the rate of efficiency and sensitivity of the system. Materials and Methods: In this study, a combination of three sources, which are Radio Frequency (RF), thermal energy and vibration are used as the input of energy harvester. Input of the thermal energy is in the Direct Current (DC) form and the voltage is set to 0.02 V. In contrast, the energy harvester of vibration and RF energy provides inputs of Alternating Current (AC) form. The RF energy harvester using input power as low as -20 dBm, which is equivalent to 32 mV at an operating frequency of 915 MHz while vibration energy harvester is set to 0.5 V at an operating frequency of 10 Hz. A full-wave rectifier is used in the vibration energy harvester to convert AC signal to DC signal. Meanwhile, RF energy harvester uses voltage multiplier circuit because it is capable to double the input voltage and rectify the voltage simultaneously. The voltage multiplier circuit is built using a substrate modulation technique. The voltage adder circuit is one of the most important part of energy harvesting circuit to integrate all the individual energy harvester circuits into a single system. All the circuits are designed, modeled and simulated using PSPICE software. Results: This system is able to achieve approximately 2.8 V output voltage across the resistor load of 1 M. Conclusion: The combination of all the energy sources; RF, vibration and thermal energy has been able to produce sufficient output voltage to power the biomedical devices.