The first experimental investigation has been made of the time‐resolved soft x‐ray spectra from an empty highZcavity target irradiated by 0.53‐&mgr;m wavelength laser. The soft x‐ray emission spectra are compared with those from planar targets with respect to temporal and spectral profiles and brightness temperature. Evidence on the radiation confinement and the plasma confinement in the cavity geometry is discussed in conjunction with the energy dissipation flow.