We present results of PAC measurements in heavy-fermion compound Yb(4)
AS(3). The quadrupole hyperfine interaction has been investigated over
the temperature range 78-850 K. The interpretation of the experimenta
l data yields a microscopic proof of the existence of a charge-ordered
state with periodic arrangement of Yb2+ and Yb3+ ions in the low temp
erature phase. In the high temperature phase all Yb ions are in a vale
nce fluctuating state.