We investigate the properties of charge–neutral \beta –equilibrium cold quark matter within the Nambu–Jona-Lasinio model .
The calculations are carried out for different ratios of coupling constants characterizing the vector and scalar 4–fermion interaction , \xi \equiv G _ { V } / G _ { S } .
It is shown that for \xi < 0.4 matter is self–bound and for \xi < 0.65 it has a first order phase transition of the liquid–gas type .
The Gibbs conditions in the mixed phase are applied for the case of two chemical potentials associated with the baryon number and electric charge .
The characteristics of the quark stars are calculated for \xi = 0 , 0.5 and 1 .
It is found that the phase transition leads to a strong density variation at the surface of these stars .
For \xi = 1 the properties of quark stars show behaviors typical for neutron stars .
At \xi \raisebox { -2.15 pt } { $ \stackrel { > } { \scriptstyle \sim } $ } 0.4 the stars near to the maximum mass have a large admixture of strange quarks in their interiors .

PACS number : 14.65.-q , 26.60.+c , 97.10.-q