Recent observations of NIR and X-ray flares from Sgr A*, the compact radio source associated with the supermassive black hole in the Galactic Center, suggest that the emission is produced via thermal synchrotron and synchrotron self-Comptonization processes. Then the size of the emission region, the electron temperature and density, and the magnetic field can be measured via simultaneous spectroscopic observations in the both bands. The flares are likely triggered by enhancements of accretion onto the black hole, and the electrons are presumably heated by the gravitational energy release of the accretion flow. From the measured electron temperature, a low bound of the energy release rate, which is related to the black hole spin, can be inferred. I will discuss how the model may be tested by observations and what needs to be done to before the spin of the black hole can be measured.