The full set of hydrodynamic equations governing the oscillation of a bubble
are solved numerically by using a modified equation of state with ionization.
We show that the hydro-thermal process in the form of compression wave and
low-level ionization is dominant inside a sonoluminescing bubble for a wide
range of driving pressures. The resulting thermal Bremsstrahlung radiation
can have pulse heights and widths that agree with available data.