  We have performed x-ray absorption spectroscopy (XAS) and x-ray photoemission
spectroscopy (XPS) studies of single crystal Ba_{1-x}K_{x}BiO_{3} (BKBO)
covering the whole composition range $0 \leq x \leq 0.60$. Several features in
the oxygen 1\textit{s} core XAS spectra show systematic changes with $x$.
Spectral weight around the absorption threshold increases with hole doping and
shows a finite jump between $x=0.30$ and 0.40, which signals the
metal-insulator transition. We have compared the obtained results with
band-structure calculations. Comparison with the XAS results of
BaPb_{1-x}Bi_{x}O_{3} has revealed quite different doping dependences between
BKBO and BPBO. We have also observed systematic core-level shifts in the XPS
spectra as well as in the XAS threshold as functions of $x$, which can be
attributed to a chemical potential shift accompanying the hole doping. The
observed chemical potential shift is found to be slower than that predicted by
the rigid band model based on the band-structure calculations.
