Static properties of the Frenkel-Kontorova model are studied by the Monte Carlo simulation : from calculations of the temperature dependent specific heat, a distribution map of number of peaks is shown in the rho-U-nor plane, with rho and U-nor being the concentration and normalized substrate potential, respectively. There exist regions of single peak, two peaks, and three peaks. The three peaks of the specific heat are discussed for rho=7/10. The physical mechanism of the peaks is investiged with the help of the static structure factors.