We have investigated the thermodynamic and structural properties of types I and II silicon clathrates through Monte Carlo simulations. Using efficient methods to determine free energies, we studied the stable and metastable relations between the various phases of Si, namely, crystalline, liquid, amorphous, and the two types of clathrates, at zero pressure. We determined the melting point of Si-46 (type I) and Si-34 (type II) clathrate structures to be at 1482 +/- 25 and 1522 +/- 25 K, respectively. Our result for the melting point of Si-34 is in good agreement with the experimental value of 1473 K. Our results also indicate that both clathrate forms are more stable than amorphous silicon for any temperature up to their melting point.7415