A census of massive galaxies at redshift increasingly higher than z \sim 1 may provide strong constraints on the history of mass assembly and of star formation .
Here we report the analysis of three galaxies selected in the Hubble Deep Field South at Ks \leq 22 on the basis of their unusually red near-IR color J-K \geq 3 .
We have used population synthesis models to constrain their redshifts and their stellar masses .
One galaxy ( HDFS-1269 ) is at redshift z _ { phot } \simeq 2.4 
while the other two ( HDFS-822 and HDFS-850 ) are at z _ { phot } \simeq 2.9 - 3.0 .
All three galaxies have already assembled a stellar mass of about 10 ^ { 11 } M _ { \odot } at the observed redshift placing the possible merging event of their formation at z \lower 3.225 pt \hbox { $ \sim$ } \hbox to 0.0 pt { \raise 1.161 pt \hbox { $ > $ } } 3.5 .
The inferred mass weighted age of their stellar populations implies that the bulk of the stars formed at z _ { f } > 3.5 .
The resulting co-moving density of \mathcal { M } _ { stars } \lower 3.225 pt \hbox { $ \sim$ } \hbox to 0.0 pt { \raise 1.161 pt% \hbox { $ > $ } } 10 ^ { 11 } M _ { \odot } 
galaxies at \langle z \rangle \simeq 2.7 is \rho = 1.2 \pm 0.7 \times 10 ^ { -4 } Mpc ^ { -3 } , about a factor two higher than the predictions of hierarchical models .
The comparison with the local density of galaxies implies that the three galaxies must have already formed most of their stellar mass and that they can not follow an evolution significantly different from a passive aging .
The comparison with the density of local L \geq L ^ { * } early types ( passively evolved galaxies ) suggests that their co-moving density can not decrease by more than a factor 2.5-3 from z = 0 to z \simeq 3 
suggesting that up to 40 % of the stellar mass content of bright ( L \geq L ^ { * } ) local early type galaxies was already in place at z > 2.5 .