IC/package radiation from a self-designed inverter chip bonded to a PCB was measured, and the radiation mechanism was investigated. Digital signals from ICs can have wide-spread frequency spectrums, and radiated signals in the radio frequency range can be picked up by other radio receivers, which causes radio-frequency interference problems. First, an equivalent radiation source for an inverter chip bonded to a PCB is reconstructed based on near-field patterns measured above the chip. The validity of the reconstructed source is proved by comparing the coupled voltage measured on a victim antenna and the voltage calculated based on the reconstructed radiation source. Then, the radiation mechanism is investigated by analyzing the equivalent radiation source as well as the signal and return current paths in full-wave simulations. Then, the critical current paths responsible for the radiation are identified. Finally, a simplified model is proposed to calculate the equivalent radiation source, with which the errors between the simplified model and full-wave simulation results were found to be within 5%.