A Compton camera is a gamma-ray imager which works in sub-MeV/MeV energy band. Up to the present, all-sky monitor COMPTEL onboard NASA's CGRO satellite has been only successful Compton camera for practical use. It consists of an upper array of liquid scintillation detectors and a lower array of NaI scintillation detectors with separation by a distance of 1.5 meter. The COMPTEL was a great contributor in high energy astrophysics, but, such massive and 1.5 ton class system is not suitable for other applications. Moreover, the lower detection threshold was limited to 750 keV due to the high threshold of 50 keV at the upper liquid scintillators. For the next generation of Compton camera, it seems to be definitely required to compress imaging system and improve the detection threshold to advance into potential gamma-ray imaging fields such as molecular imaging, nuclear medicine and security. Our group has been developed a novel Compton camera which consists of Si and CdTe semiconductor detectors. Original technologies of low noise double-sided silicon strip and CdTe pixel devices and dedicated low-noise analog ASICs allow tracking low energy gamma-ray with energy of several tens keV. We focus on the our developments of Si and CdTe semiconductor detectors and its application to medical imaging with a prototype camera in this presentation. The experimental results of imaging multiple radiopharmaceuticals injected into a living mouse is reported. Unlike astrophysical observation, the targets are located at very near-field with a distance of a few cm from the camera. By adopting near-field back-projection algorithm verified by phantom experiments, the accumulations of both Iodinated (131-I, 364 keV) methylnorcholestenol into a thyroid and adrenals and 85-Sr (514 keV) into skull, spine, lumbar and femur are clearly identified. In addition to the near-field imaging, we discuss the detection capability of radioisotopes which distribute in relatively large site with a scale of 10 to 100 meter by using the informations from multiple camera configuration. Such middle range imaging technique is expected to contribute to security and non-destructive inspection by monitoring hot spots inside buildings or containers.