The heating of matter by a source of intense x rays is studied under conditions where the energy transport in the hot material is carried by the flux of incident photons. This leads to the formation of a self‐similar heating wave. Particular emphasis is given to the ablative heating wave that exists for a time interval in between supersonic heating initially and diffusive heat transport at later times. An approximate, analytic solution of the similarity equations describing the ablative heating wave is given. A power law dependence of the opacity on temperature and density is assumed, which is strictly valid for a fully ionized plasma and monochromatic incident radiation, but possibly also useful to model more complicated situations in terms of effective parameters.